Epidemiology of muscle injuries in professional football (soccer)

Management of Proximal Hamstring Injuries: Non-operative and Operative Treatment

PURPOSE OF REVIEW

To evaluate the current evidence and literature on treatment options for proximal hamstring injuries.

RECENT FINDINGS

Patients with 3-tendon complete tears with greater than 2 cm of retraction have worse outcomes and higher complication rates compared to those with less severe injuries. Endoscopic and open proximal hamstring repair both have favorable patient reported outcomes at 5-year follow up. Proximal hamstring repair in patients who are male, with isolated semimembranosus injury, and have proximal hamstring free tendon rupture are more likely to have earlier return to sports. The Parisian Hamstring Avulsion Score (PHAS) is a validated patient-reported outcome measure to predict return to sports. Proximal hamstring injuries may occur in both elite and recreational athletes and may present with varying degrees of chronicity and severity. Injuries occur most commonly during forceful eccentric contraction of the hamstrings and often present with ischial tuberosity tenderness, ecchymosis, and hamstring weakness. Treatment decision-making is dictated by the tendons involved and chronicity. Many proximal hamstring injuries can be successfully treated with non-surgical measures. However, operative treatment of appropriately indicated proximal hamstring tendon injuries can result in significantly better functional outcomes and faster and more reliable return to sports compared to nonoperative treatment. Both endoscopic and open surgical repair techniques show high satisfaction levels and excellent patient-reported outcomes at short- and mid-term follow-up. Postoperative rehabilitation protocols vary across the literature and ongoing study is needed to clarify the optimal program, though emphasis on eccentric hamstring strengthening may be beneficial.

Different anatomic patterns of the indirect tendon of the rectus femoris

PURPOSE

The rectus femoris forms the anterior portion of the quadriceps muscle. It has a proximal tendinous complex, which is constituted by a direct tendon, an indirect tendon, and a variable third tendon. Direct and indirect tendons converge into a common tendon. The purposes of this study are to add anatomical knowledge about the proximal tendinous complex and describe anatomical variants of the indirect tendon and, on these basis, categorize different anatomical patterns.

METHOD

In this study, 48 hemipelvis from bodies donated to the Universitat Autònoma de Barcelona have been dissected to examine the proximal tendinous complex of the rectus femoris.

RESULTS

The following anatomical variants of the indirect tendon were described: inferior aponeurotic expansion in 23/48 cases (47.9%); superior aponeurotic expansion in 21/48 cases (43.7%); and an unusual origin of the myotendinous junction of the rectus femoris in the free portion of the indirect tendon in 19/48 cases (39.6%). On the basis of the aponeurotic expansions, the following anatomical patterns of the indirect tendon were defined: standard (19/48 cases, 39.6%), superior and inferior complex (15/48 cases, 31.2%), inferior complex (8/48 cases, 16.7%), and superior complex (6/48 cases, 12.5%).

CONCLUSION

We can categorize four different anatomical patterns of the indirect tendon, three of which are complex. We suggest that complex patterns can cause an increased stiffness of the indirect tendon and so be considered non-modifiable risk factors for rectus femoris injuries. Finally, it would be useful to identify complex patterns and perform injury prevention actions through specific physical preparation programs.

Guide to Muscular Injuries and Common Ligamentous Injuries Among Soccer Players

With over 250 million players worldwide, soccer is the most popular sport in the world. The overall number of players at professional, amateur, and recreational levels has increased along with an increase in player diversity, including age and sex. These increases in player numbers, as well as a variety of demographics, have resulted in an increase in soccer-related injuries. Injury in the professional setting can lead to time off the field and an effect on team results and earnings. Injury at the amateur and recreational levels can lead to time off work, away from other activities, and change in activities of daily living. We provide an extensive list of common injuries sustained by soccer players, their pathophysiology, diagnosis, treatment, and general guidelines on return to play.

Outcomes of Activity-Related Lower Extremity Muscle Tears After Application of the British Athletics Muscle Injury Classification: A Systematic Review

CONTEXT

Muscle injury classification and grading systems have been reported for >100 years; yet it offer limited evidence relating the clinical or radiological qualities of a muscle injury to the pathology or clinical outcome. The British Athletics Muscle Injury Classification (BAMIC) incorporates recent predictive features of muscle injuries and provides a precise radiographic framework for clinical prediction and management.

OBJECTIVE

To investigate clinical outcomes, particularly time to return to play (RTP), reinjury rate (RIR), and prognostic value of specific magnetic resonance imaging (MRI) findings, of activity-related muscle injuries (tears) in athletes after application of the BAMIC.

DATA SOURCES

A search of PubMed (NLM), EMBASE (Ovid), Web of Science (Clarivate), Cochrane Library (Wiley), and ClinicalTrials.gov from the inception date of each database through August 31, 2022, was conducted. Keywords included the BAMIC.

STUDY SELECTION

All English language studies evaluating clinical outcomes of RTP and RIR after activity-related muscle injuries and where BAMIC was applied were included. A total of 136 articles were identified, and 11 studies met inclusion criteria.

STUDY DESIGN

Systematic review (PROSPERO: CRD42022353801).

LEVEL OF EVIDENCE

Level 2.

DATA EXTRACTION

Two reviewers independently screened studies for eligibility and extracted data. Methodological quality of included study was assessed independently by 2 reviewers with the Newcastle-Ottawa Quality Scale (NOS); 11 good quality studies (4 prospective cohort studies, 7 retrospective cohort studies) with 468 athletes (57 female) and 574 muscle injuries were included.

RESULTS

All studies reported a statistically significant relationship between BAMIC grade, BAMIC injury site, and/or combined BAMIC grade and injury site with RTP. A statistically significant increased RIR was reported by BAMIC grade and BAMIC injury site in 2 of 4 and 3 of 4 studies, respectively. The prognostic value of individual MRI criteria was limited.

CONCLUSION

Consistent evidence suggests that BAMIC offers prognostic and therapeutic guidance for clinical outcomes, particularly RTP and RIR, after activity-related muscle injuries in athletes that may be superior to previous muscle injury classification and grading systems.

Epidemiology of Hamstring Tears in National Collegiate Athletic Association Athletes: Findings From the National Collegiate Athletic Association Injury Surveillance Program Between 2014/2015 and 2018/2019

OBJECTIVE

To describe the epidemiology of hamstring tears in National Collegiate Athletic Association (NCAA) sports.

DESIGN

Descriptive epidemiology study. Athletic trainers from NCAA schools reported injuries to the NCAA Injury Surveillance Program.

SETTING

A convenience sample of NCAA hamstring tear injuries during the 2014/2015 through 2018/2019 academic years.

PATIENTS OR PARTICIPANTS

NCAA student-athletes.

INDEPENDENT VARIABLES

Sport, sex, event type, season segment, injury history, and activity at the time of injury.

MAIN OUTCOME MEASURES

Injury counts, rates, and proportions were used.

RESULTS

Two thousand ninety-six hamstring tears from 8 474 400 athlete-exposures (AEs) were reported (2.47 per 10 000 AEs). Rates were highest in Men's Soccer (5.97 per 10 000 AEs) and Women's Soccer (3.13 per 10 000 AEs), among all Men's and Women's sports, respectively. Competition-related rates in Men's and Women's sports were highest in 2015 to 2016 then followed a decreasing pattern across the remainder of the study period. Among sex-comparable sports, rates were higher in men's (compared with women's) Baseball/Softball, Soccer, and Track and Field. The prevalence of recurrent injuries was comparable among men's (14.8%) and women's (11.5%) sports. Time loss hamstring tears were more prevalent in Men's sports than Women's sports [injury proportion ratio = 1.33; 95% confidence interval, (1.21, 1.47)].

CONCLUSIONS

Overall, hamstring tear rates were higher across all Men's sports compared with Women's sports. Rates across event type were comparable in several sports; and so, adjustments to practice are needed considering that practice environments are more modifiable than competitions. Indeed, improving hamstring tear prevention programs to reduce the burden of this injury in NCAA athletes remains critical.

Characterization of acute effects of football competition on hamstring muscles by muscle functional MRI techniques

Muscle functional MRI identifies changes in metabolic activity in each muscle and provides a quantitative index of muscle activation and damage. No previous studies have analyzed the hamstrings activation over a football match. This study aimed at detecting different patterns of hamstring muscles activation after a football game, and to examine inter- and intramuscular differences (proximal-middle-distal) in hamstring muscles activation using transverse relaxation time (T2)-weighted magnetic resonance images. Eleven healthy football players were recruited for this study. T2 relaxation time mapping-MRI was performed before (2 hours) and immediately after a match (on average 13 min). The T2 values of each hamstring muscle at the distal, middle, and proximal portions were measured. The primary outcome measure was the increase in T2 relaxation time value after a match. Linear mixed models were used to detect differences pre and postmatch. MRI examination showed that there was no obvious abnormality in the shape and the conventional T2 weighted signal of the hamstring muscles after a match. On the other hand, muscle functional MRI T2 analysis revealed that T2 relaxation time significantly increased at distal and middle portions of the semitendinosus muscle (p = 0.0003 in both cases). By employing T2 relaxation time mapping, we have identified alterations within the hamstring muscles being the semitendinosus as the most engaged muscle, particularly within its middle and distal thirds. This investigation underscores the utility of T2 relaxation time mapping in evaluating muscle activation patterns during football matches, facilitating the detection of anomalous activation patterns that may warrant injury reduction interventions.

The isometric and isokinetic knee extension and flexion muscle strength profile of elite soccer players

BACKGROUND

This study aimed to further complete normative data sets for the strength profile of the thigh in soccer players by performing isometric and isokinetic measurements in a large sample per player position.

METHODS

In total, 364 soccer players were divided into subgroups according to their pitch position. All players performed isometric and isokinetic strength measurements during active competition period using an isokinetic dynamometer (System 3, Biodex®, ENRAF-NONIUS, New York, USA).

RESULTS

Isokinetic strength of m. Quadriceps was significantly (p = 0.023) higher in strikers compared to central midfielders in both the dominant (+ 9%) and the non-dominant (+ 4%) leg. No further differences were found in isometric or isokinetic strength per playing positions.

CONCLUSIONS

We have shown that strength profiles do not differ between playing positions on the field. This is valuable information for elite soccer high performance coaches and medical staffs aiming to improve daily training efficiency and rehabilitation of their players.

Correlation of Player and Imaging Characteristics With Severity and Missed Time in National Football League Professional Athletes With Hamstring Strain Injury: A Retrospective Review

BACKGROUND

Hamstring strain injuries (HSIs) are prevalent in US National Football League (NFL) players, but there is a paucity of information regarding imaging characteristics, injury severity, and player factors associated with time missed and risk of recurrent injury.

PURPOSE

To describe player, football activity, clinical, and imaging characteristics of NFL players with HSIs, as well as determine player characteristics, clinical examination results, and magnetic resonance imaging (MRI) findings associated with injury occurrence, severity, and missed time.

STUDY DESIGN

Cross-sectional study; Level of evidence, 3.

METHODS

A retrospective cohort of NFL players with acute HSI (n = 180) during the 2018-2019 season was identified. Injury data were collected prospectively through a league-wide electronic health record system. Three musculoskeletal radiologists graded MRI muscle injury parameters using the British Athletics Muscle Injury Classification (BAMIC) system. Player, football, clinical, and imaging characteristics were correlated with HSI incidence and severity and with missed time from sport.

RESULTS

Of the 1098 HSIs identified during the 2018-2019 season, 416 (37.9%) were randomly sampled, and 180 (43.3%) had diagnostic imaging available. Game activity, preseason period, and wide receiver and defensive secondary positions disproportionately contributed to HSI. The biceps femoris was the most commonly injured muscle (n = 132, 73.3%), followed by the semimembranosus (n = 24, 13.3%) and semitendinosus (n = 17, 9.4%) muscles. The most common injury site was the distal third of the biceps femoris and semitendinosus muscles (n = 60, 45.5% and n = 10, 58.8%, respectively) and central part of the semimembranosus muscle (n = 17, 70.8%). Nearly half of the injuries (n = 83, 46.1%) were BAMIC grade 2; 25.6% (n = 46), grade 3; and 17.8% (n = 32), grade 4. MRI showed sciatic nerve abnormality in 30.6% (n = 55) of all HSIs and 81.3% (n = 26) of complete tendon injuries. BAMIC grade correlated with both median days and games missed. Combined biceps femoris and semitendinosus injuries resulted in the highest median days missed (27 days).

CONCLUSION

Among NFL players with acute HSIs, the most common injury was a moderate-severity injury of the distal biceps femoris. BAMIC grade was associated with missed time.

Mitigating the Risks of Lower Extremity Injuries in Soccer: A Comprehensive Analysis of Lower Extremity Injury Rates in Soccer Between 2014 and 2023

Objective

With events such as the Copa America 2024, the 2026 World Cup, and the arrival of European stars in Major League Soccer (MLS), the already observed and forecasted rise of soccer in the United States (US) seems to be an inevitable outcome. Although regular participation in soccer features several benefits, including increasing cardiovascular health, decreasing stress, and promoting interpersonal relationships, the risk of injury, as is the case in any sport, is ever present. Although many sports that are popular in America feature high rates of concussion, rotator cuff injuries, and general upper extremity injuries, soccer, being more strenuous on the lower-half of the body, features a disproportionate rate of lower extremity injuries. An analysis of the frequencies of these injuries, relative to factors such as year of injury, age, gender, location of injury, and diagnosis of injury, may help organizational bodies and soccer leagues implement new regulations regarding the usage of protective equipment and rules regarding gameplay. This study aims to illuminate these takeaways in an effort to better patient care outcomes in soccer-related injuries.

Method

This paper utilized the National Electronic Injury Surveillance System Database (NEISS) to compile data on lower extremity soccer-related injuries within the defined study period, 2014-2023. Inclusion criteria for the study involved all patients presenting to the emergency department (ED) within the study period and within the defined age range of 0 to 69 years old, with injuries sustained from or related to soccer. Using NEISS, trends were elucidated discriminating based on year of injury, sex, age group, location of injury, and diagnosis group of injury.

Results

Within the defined study period of 10 years, from 2014-2023, there were approximately 843,063 total soccer-related lower extremity injuries which presented to various EDs across the US. Regarding majorities, the most injuries were sustained in 2014 (12.84% of total injuries), most patients sustaining injuries were male (66.6% of all patients), and within the age range of 10-19 years old (63.24% of all patients), with the most instances occurring at age 15. Lower extremity injuries were most reported to be affecting the ankle with 306,797 incidences (36.39% of total injuries seen) and the most frequent diagnosis group was reported to be strains/sprains with 396,420 (47.02% of total injuries seen) total occurrences.

Conclusion

This study analyzes the incidents of lower extremity injuries while participating in soccer for the last 10 years, 2014-2023. The study provides new data regarding the frequency of injuries and their relative rate with respect to year of injury, age group, sex, location of injury, and diagnosis. The results of this study show injury majorities and trends which can be used to dictate changes in regulation regarding gameplay and the utilization of protective equipment in order to mitigate injuries related to the lower extremities in soccer.

Deceleration Capacity During Directional Change as a Time-Efficient (Ecological) Prescreening of Hip Adductor Force Status in Amateur Soccer Players

ABSTRACT

Miralles-Iborra, A, Del Coso, J, De Los Ríos-Calonge, J, Elvira, JLL, Barbado, D, Urban, T, and Moreno-Pérez, V. Deceleration capacity during directional change as a time-efficient (ecological) prescreening of hip adductor force status in amateur soccer players. J Strength Cond Res XX(X): 000-000, 2024-Reduced isometric adductor muscle strength has been identified as a modifiable risk factor contributing to injury in soccer players. However, the measurement of hip adductor muscle strength is habitually laboratory-based, with isolated hip movements that do not reflect soccer-specific movements that induce groin injury during match play. This study aimed to determine the usefulness of deceleration capacity during a change of direction (COD) as a time-efficient (ecological) prescreening of hip adductor force status in soccer players. Nineteen amateur soccer players completed unilateral isometric hip adductor strength assessments and a 180° COD test. Isometric hip strength assessment included the maximum peak torque (PT) and maximum rate of torque development (RTDmax) relative to players' body mass. Players' deceleration capacity during the COD test was determined for each leg through maximum deceleration normalized to the linear momentum. A linear regression analysis was performed to associate isometric hip strength variables with the deceleration capacity during the COD test at each leg. There was not a statistically significant association between deceleration capacity and hip isometric maximum PT of the dominant and nondominant legs (r ≤ 0.14, p > 0.05). Nevertheless, a moderate association was found between deceleration capacity and RTDmax for both legs (r ≥ 0.58, p < 0.05). The optimal linear regression model suggests that measuring deceleration capacity during a directional change test could explain RTDmax by 33 and 43% for the dominant and nondominant legs, respectively. During a 180° COD test, the deceleration capacity captured through GPS-accelerometer device was limited as a prescreening tool to evaluate hip adductor force status in soccer players.

Secondary injury prevention reduces hamstring strain and time-loss groin injury burdens in male professional football

OBJECTIVES

This study aimed to assess the effectiveness of a systems-based secondary injury prevention intervention aimed at early detection and management of hamstring strain injury (HSI) and time-loss groin injury in an Australian male professional football club.

DESIGN

Prospective cohort study.

SETTING

Australian male professional football club.

PARTICIPANTS

Data were collected from male professional football players (n = 73) from a single football club.

MAIN OUTCOME MEASURES

Unilateral knee flexion and side-lying hip adduction maximum voluntary isometric contractions were monitored routinely in-season, two days post-match (≥40 h [h]) during a three-season intervention period. Strength reductions greater than the tests' minimal detectable change percentage prompted intervention. HSI and time-loss groin injury burdens were calculated per 1000 player hours and compared with those from an immediately preceding two-season control period, to assess the effectiveness of the intervention.

RESULTS

Across the intervention period, there was a decrease in HSI (4.98 days absence/1000 h (19.8%) decrease) and time-loss groin injury burdens (0.57 days absence/1000 h (49.1%) decrease) when compared with the control period.

CONCLUSIONS

A systems-based secondary injury prevention intervention shows preliminary positive findings in reducing HSI and time-loss groin injury burdens within a male professional football club, compared with usual care only.

A criteria-based progressive rehabilitation program for rectus femoris strain in a recreational soccer player: a case report

Introduction: The purpose of this study was to describe the criteria-based progressive rehabilitation program implemented on a recreational soccer player diagnosed with a grade 1 rectus femoris strain. Methods: A 33-year-old male injured the rectus femoris muscle. At the first physical examination, the patient showed significant physical impairment due to important limitations to the active range of motion of the knee flexion and the hip flexor strength. The rehabilitation program consisted of specific training of the rectus femoris, lumbopelvic stabilization, mobility exercises, and running technique exercises, for 6 weeks, which was divided into three phases. Each week, the patient performed four rehabilitation sessions, combined with cross-training (swimming), to maintain his cardiorespiratory capacity. Results: The patient improved functionally and returned to play soccer 6 weeks after the injury without pain. Moreover, the patient passed the criteria of each phase at week 2 for phase 1, at week 4 for phase 2 and at week 6 for phase 3. Conclusion: This case study demonstrates that criteria of progression may control the return to sport timetable for recreational soccer players according to the functional and clinical limitations throughout the entire treatment.

ORTHOPEDIC INJURIES IN MEN'S PROFESSIONAL SOCCER DURING THE CORONAVIRUS DISEASE PANDEMIC

Objective

To assess the incidence and characteristics of injuries that occurred in the 2020 season of the Paulista Football Championship during the novel coronavirus disease pandemic.

Methods

We conducted a prospective study using an electronic questionnaire developed by the Medical Committee of the Paulista Football Federation. Results were sent to the team doctors of series A1 and A2 after each round of the Paulista Football Championship.

Results

Series A1 and A2 presented 12.17 and 15.6 injuries, respectively, per 1000 gaming hours. The strikers were the most affected, with muscle injuries being the most frequent and the lower limbs being the most affected. Most injuries occurred within 31-45 minutes of playing; only 4.5% of injuries required surgery.

Conclusion

There was no statistical difference in the comparison between pre- and post-pandemic conditions. In relation to the variables studied, the most injuries occurred in the lower limbs; the most common type of injury was muscle strain, followed by sprain and contusion. The most requested exam was MRI; most injuries were classified as moderate (8-28 days). There was no difference between pre- and post-pandemic conditions. Level of Evidence IV, Case Series.

Assessing Lower-Extremity Visuo-Motor Reaction Time in Young Male Soccer Players: Test-Retest Reliability and Minimum Detectable Change of the Brain Pro System

A reliable, versatile means of assessing visuo-motor reaction time (V-MRT) is important to football (soccer) players for many reasons, including the fact that faster V-MRT is a critical sport skill that may even play a role in reducing common sports injuries to the lower muscle extremities that can be associated with lost time on the field. We aimed to determine the test-retest reliability and minimum detectable change (MDC) of the Brain Pro System for assessing lower-extremity V-MRT in young male football players. We had 68 participants (M age = 16.35, SD = 1.71 years) perform two assessment sessions one-week apart. For test-retest reliability, we calculated a one-way intra-class correlation coefficient (ICC) at the 95% confidence interval and provided the standard error of measurement (SEM) and minimum detectable change (MDC) (MDC = SEM × 1.96 × √2) for V-MRTs. We obtained excellent V-MRT test-retest reliability for dominant lower-extremity, non-dominant lower-extremity, and dominant and non-dominant lower-extremities (ICC2,1 = .93, 95%CI = .89-.96; ICC2,1 = .94, 95%CI = .91-.96; ICC2,1 = .96, 95%CI = .94-.97; respectively). The calculated MDC for the dominant lower-extremity V-MRT, the non-dominant lower-extremity V-MRT, and dominant and non-dominant lower-extremities (random) V-MRT were 1.21 seconds, 1.13 seconds, and 1.21 seconds, respectively. Brain Pro System had excellent reliability for assessing lower-extremity V-MRT in young male football players. The MDC values at the 95% confidence level (MDC95) we obtained were reliable for assessing clinically meaningful V-MRT changes.

Predicting the occurrence of in-season groin pain in male high school soccer players: a cohort study

[Purpose] This study investigated whether pre-season HAGOS (Japanese Copenhagen Hip and Groin Outcome Scores) and eccentric muscle strength of the hip muscles predict in-season groin pain incidences in high school soccer players. [Participants and Methods] This study had a cohort design. The participants were male high school players under 18 years playing in the Japan Soccer League, which is an elite-level soccer league of that age category in Japan. The HAGOS and the strength of hip abductor and adductor muscles in eccentric contraction were measured before the season, and hip and groin pain incidences were recorded during the season. Multiple logistic regression analysis was performed to investigate the factors derived from the pre-season HAGOS and hip muscle strength tests, presumably pertaining to the development of in-season groin pain. [Results] The eccentric adductor muscle strength of the dominant leg and the HAGOS were selected as factors associated with groin pain during the season. [Conclusion] Low pre-season HAGOS and weak dominant-leg eccentric adductor muscle strength were suggested as factors to predict in-season groin pain occurrence in male high school soccer players.

Muscle Healing in Sports Injuries: MRI Findings and Proposed Classification Based on a Single Institutional Experience and Clinical Observation

MRI plays a crucial role in assessment of patients with muscle injuries. The healing process of these injuries has been studied in depth from the pathophysiologic and histologic points of view and divided into destruction, repair, and remodeling phases, but the MRI findings of these phases have not been fully described, to our knowledge. On the basis of results from 310 MRI studies, including both basal and follow-up studies, in 128 athletes with muscle tears including their clinical evolution, the authors review MRI findings in muscle healing and propose a practical imaging classification based on morphology and signal intensity that correlates with histologic changes. The proposed phases, which can overlap, are destruction (phase 1), showing myoconnective tissue discontinuity and featherlike edema; repair (phase 2), showing filling in of the connective tissue gaps by a hypertrophic immature scar; and remodeling (phase 3), showing scar maturation and regression of the edema. A final healed stage can be identified with MRI, which is characterized by persistence of a slight fusiform thickening of the connective tissue. This information can be obtained from a truncated MRI protocol with three acquisitions, preferably performed with a 3-T magnet. During MRI follow-up of muscle injuries, other important features to be assessed are changes in muscle edema and specific warning signs, such as persistent intermuscular edema, new connective tear, and scar rupture. An understanding of the MRI appearance of normal and abnormal muscle healing and warning signs, along with cooperation with a multidisciplinary team, enable optimization of return to play for the injured athlete. ©RSNA, 2024 See the invited commentary by Flores in this issue.

The Effects of Nordic Hamstring Exercise on Performance and Injury in the Lower Extremities: An Umbrella Review

Due to their potential positive outcomes, hamstring eccentric exercises are becoming increasingly popular in training regimens. Among the various exercises, the Nordic Hamstring Exercise (NHE) is the most common. Despite its popularity, there are still some doubts about its benefits and risks. So, the aim of this umbrella review was to summarize the effects of NHE on performance and injury prevention. Following the PRISMA guidelines, a comprehensive literature search was conducted across multiple e-databases, according to the P (injured and non-injured athletes or recreationally active or healthy individuals) I (NHE) C (no intervention, placebo, or other interventions) O (performance or injury) S (systematic reviews) model. The quality of the studies was accessed with the AMSTAR-2. From the 916 systematic reviews found, only 10 could be included. They encompassed 125 studies, enrolling 17,260 subjects. The results from the studies indicate that NHE interventions demonstrated positive effects on sprint performance, muscle activation, eccentric strength, and muscle architecture (fascicle length, muscle thickness, and pennation angle). Furthermore, NHE is effective in preventing hamstring injuries (up to 51%). In conclusion, NHE should be integrated in training (especially, in the warm-up phase) for both enhancing athletic performance and preventing hamstring injuries. For achieving more positive results, it is recommended that high-volume is followed by low-volume maintenance, targeting 48 reps/week.

Performing Lower-Limb Strength Exercises Before or After Training Does not Influence Fatigue Indices in Competitive Youth Soccer Players

ABSTRACT

Gantzer, C, Huff, D, Butterick, B, Chalmers, S, Marshall, P, Lovell, R, and Siegler, JC. Performing lower-limb strength exercises before or after training does not influence fatigue indices in competitive youth soccer players. J Strength Cond Res XX(X): 000-000, 2024-A multicenter approach was used to conduct a controlled, laboratory-based study (Part A) in conjunction with an ecologically focused, field-based study (Part B) of the influence of timing on hamstring fatigue induced by lower-limb strength exercises. Part A required players to perform the FIFA 11+ warm-up before a simulated soccer training session, whereas the other session involved removing the lower-limb strength exercises from the warm-up and delivering them after the simulated session. For Part B, players completed 2 live training sessions, where one session included the Nordic hamstring exercise (NHE) as part of a standardized warm-up before training and the other session incorporated the NHE at the end of training. Maximal hamstring force (MVC), rate of force development (RFD), countermovement jump (CMJ), and sprint speed (SS) were assessed before, during, and after the simulation and field training, respectively, to quantify fatigue across both study cohorts. There was no suggestion that timing of the intervention had an influence fatigue in either Part A or B, with no condition (MVC [Part A & B]: p > 0.43; RFD: p = 0.43; CMJ: p = 0.10; SS: p = 0.62), time (MVC: p > 0.30; RFD: p = 0.72; CMJ: p = 0.87; SS: p = 0.85), or interactions (MVC: p > 0.93; RFD: p = 0.78; CMJ: p = 0.99; SS: p = 0.94) evident. Our findings suggest youth soccer coaches should not be concerned with the timing of interventions, allowing them to focus instead on adherence and player buy-in.

The Quality of Life of Former Portuguese Football Players

BACKGROUND

The demands of playing professional football can have an impact on an individual's quality of life (QoL), which may remain into retirement. Given limited evidence exists regarding the QoL in former football players, this study aimed to assess QoL among Portuguese former players according to career duration, career end period, competitive level, tactical-positional status, international status, academic qualifications, serious injuries in career, and current professional football connection.

METHODS

The study included 84 Portuguese former football players (48.8 ± 8.2 years old) who transitioned to retirement between 1988 and 2018. The WHOQOL-BREF questionnaire was used to assess QoL perceptions, and the Portuguese version was validated.

RESULTS AND DISCUSSION

The former players have positive QoL indicators, both in general and across the four domains, namely in terms of the physical, psychological, and social relationship and environment. There were no statistically significant differences in QoL between the defined categories for career end period, competitive level, tactical-positional status, international status, and current professional football connection. Likewise, there was no significant correlation between QoL and career duration. In contrast, there were significant differences in general QoL (p < 0.023) and in the physical domain (p < 0.001) between former players with different academic qualifications. A significant correlation was found between the number of severe injuries sustained in a career and QoL in the physical domain (R = -0.300, p = 0.006).

CONCLUSIONS

There are no concerning QoL results presented by former players. However, the number of severe injuries sustained during the career was associated with a lower QoL, while holding higher academic qualifications demonstrated higher general and physical QoL. Studies with larger samples should be conducted to confirm these trends.

Degloving intramuscular injuries of the semimembranosus and adductor longus muscles in adolescent soccer players

Degloving muscle injury was described for the rectus femoris where the inner bipennate component is dissociated from its superficial unipennate component. The semimembranosus muscle displays a distinctive dual morphology, featuring both unipennate and bipennate muscle fibers. Nevertheless, this specific tear pattern has not been previously documented. Conversely, the adductor longus muscle showcases an elongated intramuscular tendon segment, indicating a multipennate morphology. We present two separate cases of previous undescribed degloving injuries of the semimembranosus and the adductor longus in teenage soccer players with MRI and ultrasound diagnosis, ultrasound-guided hematoma aspiration, and recovery timelines for return-to-play.

Assessment of Strength and Power Capacities in Elite Male Soccer: A Systematic Review of Test Protocols Used in Practice and Research

BACKGROUND

Strength and power represent two crucial physical qualities for the attainment of a high level of performance considering the frequency and the importance of explosive actions occurring during elite soccer match-play. Evaluation of strength and power is a multifaceted concept involving a vast array of tests and outcome variables. Nevertheless, a comprehensive and systematic search of strength and power assessment procedures in elite soccer has yet to be undertaken.

OBJECTIVES

The aims of this systematic review were to: (1) identify the tests and outcome variables used to assess strength and power of elite male soccer players; (2) provide normative values for the most common tests of strength and power across different playing levels; and (3) report the reliability values of these strength and power tests.

METHODS

A systematic review of the academic databases MEDLINE, CINAHL, SPORTDiscus, Web of Science and OVID for studies published until August 2023 was conducted, following the Preferred Reporting Items of Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Studies were eligible for inclusion if they: (1) were original research studies, published in a peer-reviewed journal, and written in English language; (2) had the primary aim to assess strength and/or power; (3) players were male and older than 17 years of age (i.e., mean age of the group); and (4) their playing level was defined as "professional", "international" or "elite".

RESULTS

Regarding strength testing, 115 studies and 29 different tests were identified. The three most frequent strength tests were the knee extensor isokinetic strength test (58 studies), the knee flexor isokinetic strength test (55 studies) and the Nordic hamstring strength test (13 studies). In terms of power testing, 127 studies with 31 different tests were included. The three most frequent power tests were the countermovement jump with hands fixed on hips (99 studies), the squat jump (48 studies) and the vertical jump with arm swing (29 studies).

CONCLUSIONS

The wide range of different tests and outcome variables identified in this systematic review highlights the large diversity in the employed testing procedures. The establishment of a hybrid testing approach, combining standardised and widely accepted tests for establishing normative standards and enabling comparisons across different contexts, with flexible context-specific testing batteries, has the potential to maximise the impact of testing information for practitioners. In addition, the limited reporting of reliability data across studies highlights the need for practitioners to establish their own reliability measure within their specific contexts, informing the selection of certain tests and outcome variables.

Non-surgical management of acute proximal hamstring avulsions can produce clinically acceptable results

PURPOSE

To evaluate the mid-term clinical outcomes for the non-surgical and surgical management of acute proximal hamstring avulsions.

METHODS

Sixty physically active individuals were offered surgical or non-surgical management for their proximal hamstring avulsion injuries. Distal retraction was defined as greater than 2 cm. Primary outcome measures were the Victorian Institute of sport assessment-proximal hamstring tendons (VISA-H) and functional assessment scale for acute hamstring injuries (FASH). Secondary outcome measures included palpable gap (cm), return to sport (RTS) and the ability to perform Nordic hamstring curls. Outcome variables were adjusted in regression models for gender, age, and treatment.

RESULTS

Thirty-one patients elected to undertake non-surgical management, and 29 chose surgery with a mean follow-up of 34.8 ± 8.7 and 34.9 ± 7.0 months, respectively. The mean VISA-H for the non-surgical and surgical groups were 87.3 ± 3.4 and 87.9 ± 4.1 (n.s.), respectively. The mean FASH for the non-surgical group was 89.3 ± 2.4 and 88 ± 3.6 for the surgical group (n.s.). This was consistent after adjusting for confounders. The mean gap for the non-surgical group was 4.5 ± 1.09 and 4.9 ± 1.19 cm for the surgical group (n.s.). No significant differences were found in the abilities to perform Nordic hamstring curls (n.s.). Both groups achieved comparable RTS rates (n.s.). On average, the non-surgical group achieved RTS at 5.5 ± 1.2 months post-injury, whereas the surgical group was at 5.7 ± 0.7 months (n.s.).

CONCLUSION

Physically active individuals with acute proximal hamstring avulsions and distal retraction of the tendon stump can be managed non-surgically, achieving similar functional levels and RTS compared to patients treated surgically.

LEVEL OF EVIDENCE

Level III.

Hip Sideline Emergencies and Hip Injuries in Elite Athletes

PURPOSE OF REVIEW

Hip injuries in elite athletes are an increasingly recognized problem and range from chronic overuse injuries, such as adductor strains and labral tears, to acute traumatic injuries such as hip dislocations. In this article, we review common hip pathology experienced by elite athletes and sideline management of emergent hip injuries.

RECENT FINDINGS

Elite athletes are subject to unique physical and mental stresses and therefore must be evaluated and treated in a unique manner. Hip and groin injuries account for approximately 6% of sport injuries overall and 3-15% of all injuries in professional sports. Hip sideline emergencies were rare but can include hip dislocations, subluxations, and avulsion fractures. Hip and groin injuries represent an important subset of injuries which can greatly impact an athlete's ability to perform. Understanding the physiology and types of hip/groin injuries, which athletes are prone to injuries, the impact on recovery time, recurrence risk, and the potential need for surgery aid sports medicine physicians in decision-making.

Towards a more individualised assessment of post-training fatigue in young footballers

Despite improvements in training load and fatigue monitoring, fatigue status may adversely affect intrinsic risk factors, particularly in young footballers. This study aimed to better individualise the fatigue effects of a 75-min football training session in young elite male players. Eighteen players (15.6 ± 1.7 years) completed a test battery before and after a football training session. Assessments included capillary blood samples (HCO3 -, lactate, pH), subjective ratings of muscle soreness and fatigue. Functional tests included 30 m field sprint, laboratory drop jump (DJ) and horizontal force-velocity (H-FvP). The k-means method was applied to the first two dimensions of principal component analysis of changes in the H-FvP and DJ tests. Football training resulted in significant physiological changes and functional impairments, in particular an increase in interlimb asymmetry in the DJ test. No significant fatigue effect was found on the H-FvP test data. However, confirming the interest of combining the two tests, cluster analysis revealed two subgroups: In the H-FvP test, Cluster 1 decreased inV ‾ 0 (p < 0.001) andP ‾ max (p < 0.01), while Cluster 2 decreased inF ‾ 0 (p < 0.001). In the DJ test, Cluster 1 decreased in mean velocity (p < 0.01), relative mean and maximum power (p < 0.01) during push-off, while Cluster 2 decreased in relative mean push-off force (p < 0.01) and increased in interlimb asymmetry during braking (p < 0.01). This study highlights the contribution and complementarity of the H-FvP and DJ tests to improve individual screening for fatigue-related functional changes in footballers. Extrapolated values from the H-FvP test led to the identification of two subgroups with opposite fatigue profiles. One subgroup showed increased interlimb asymmetry in DJ, indicating an increased risk of injury with fatigue. These findings highlight the need for individualised fatigue assessment in young footballers.

Semitendinosus and biceps femoris long head activity during the single leg bridge test in healthy individuals

INTRODUCTION

The single leg bridge test (SLBT) has been suggested as a clinical test to examine function, screen injury risk, and monitor the effectiveness of rehabilitation programes targeting the hamstring. This study aimed to determine the inter-day reliability and repeatability of both SLBT performance, semitendinosus (ST), and biceps femoris long head (BFlh) surface electromyography (sEMG) responses and characterise the BFlh and ST electrical activity during the SLBT performed until exhaustion in healthy individuals.

METHODS

Twelve physically active young men without previous hamstring injury were tested for the number of repetitions attained, and sEMG signal median frequency and amplitude in both ST and BFlh of each lower limb, randomly in two sessions, with a seven-day interval between sessions.

RESULTS

High reliability [ICC = 0.85] was found for the number of SLBT repetitions attained. Reliability of sEMG outcomes showed better results for ST (ICC = 0.62-0.91) than for BFlh (ICC = 0.39-0.81), and a high to very-high repeatability was found for both ST (ICC = 0.91-0.84) and BFlh (ICC = 0.91-0.85). sEMG median frequency decreased and amplitude increased for both BFlh (p ≤ 0.001) and ST (p ≤ 0.039) at the end of SLBT, suggesting localised fatigue.

CONCLUSIONS

The SLBT performed by healthy individuals until exhaustion proved to be reliable and to induce fatigue in both BFlh and ST, where the sEMG median frequency and amplitude can be measured on different days with acceptable reliability and high repeatability, suggesting its potential future use in both practical and clinical settings.

Epidemiology of Non-Contact Muscle Injuries in the Italian Male Elite Under-19 Football (Soccer) Championship

BACKGROUND

While extensive research exists on muscle injuries among adult football players, a notable gap persists in studies concerning younger footballers. The aim of the current study is to provide epidemiological data on the characteristics of time-loss muscle injuries in young football players participating in the Italian Under-19 male elite Championship ("Primavera 1").

RESULTS

Conducted as a multicentre, prospective, observational cohort study, this research gathered injury data from the 2022-23 season across 14 of the 18 Clubs in the first Italian Under-19 championship. The cohort comprised 391 players with a mean age (± standard deviation) of 18.0 ± 0.4 years. A total of 479 injuries were reported, resulting in 14,231 days of activity lost. Of these, muscle injuries were 209 (44%), accounting for 4,519 (32%) days lost. Overall muscle injuries incidence was 1.82/1000 hours, with a mean injury burden of 39.4 days lost/1000 hours. Almost all muscle injuries (206 out of 209: 98.5%) occurred in hamstrings, quadriceps, adductors, calf and iliopsoas. Hamstrings injuries were the most burdensome (18.8 days lost/1000 hours) accounting for nearly half of all days lost due to muscle injuries. Incidence and burden of adductors injuries (0.25 injuries and 4.1 days lost/1000 hours, respectively) were found to be comparable to calf injuries (0.24 injuries and 4.7 days lost/1000 hours, respectively). Iliopsoas injuries accounted for a noteworthy portion of the total, with an injury incidence of 0.16/1000 hours and a burden of 3.3 days lost/1000 hours. Injuries with myo-tendinous or myo-aponeurotic involvement demonstrated delayed return-to-football compared to those without such involvement (35.6 vs. 18.5 days, p < 0.0001).

CONCLUSIONS

The study highlighted a peculiar distribution of non-contact muscle injuries among elite young football players. While hamstring injuries were confirmed as the most burdensome, incidence and burden of adductors and calf injuries were found to be similar. A significant incidence and burden of iliopsoas injuries were observed. These findings suggest potential implementations for targeted injury prevention strategies in the Italian male elite Under-19 football Championship.

Leukocyte-Rich Platelet-Rich Plasma Injection in an Acute-on-Chronic Rectus Femoris Injury of a Professional Soccer Player: A Case Report

This is the case of an 18-year-old male professional soccer player, an attacking midfielder, who presented acute-onset pain in his right thigh during a training match but continued playing and training until the end of the session. Two weeks after the initial symptoms, the athlete's pain increased after kicking the ball and stopping training. He came for consultation a week later with tenderness in his right thigh and impaired gait. A 3 ​cm gap in his right mid-quadriceps muscle and tenderness during resisted knee extension and leg raises with no hip or knee range of motion limitations were observed on physical examination. He was scheduled for magnetic resonance imaging (MRI) after the consultation, revealing an acute-on-chronic type 2A lateral muscle tear of the distal rectus femoris. A 2 ​ml seroma aspiration was performed five weeks after the initial injury with a subsequent intra-lesional 1 ​ml liquid leukocyte-rich platelet-rich plasma (LR-PRP) injection using intermittent ultrasound guidance within 5 ​min after preparation. The LR-PRP preparation was classified as 3 14-1 3-0 0 according to the Universal Coding System (UCS) by Kon et al. Nine physiotherapy sessions, including an initial assessment, were conducted over five weeks. The rehabilitation started with pulley exercises with hip flexion, tension arch, leg extension, and squatting with supporting exercises for core and hip strength, with a gradual increase in loading. As the player's symptoms improved, he started doing eccentric exercises such as the reverse Nordics and leg extension. He also followed a running program, gradually increasing speed to a full sprint without pain or irritation. The return-to-sports clearance consultation was conducted seven weeks after the injury, previously confirming satisfactory healing on an MRI. The patient was cleared after passing the Rehabilitation Department battery tests and physical examination. The patient was asymptomatic and had no complaints despite his right quadriceps gap, returning to competition nine weeks after injury. After a one-year follow-up, the patient remains playing at a competitive level, asymptomatic, with no reported reinjury. Adequate reporting of rehabilitation programs and PRP injection characterization is crucial for future research quality improvement and reproducibility.

A comparative video analysis of hamstring injuries mechanism and situational pattern in men's and women's football (soccer)

PURPOSE

To describe the injury mechanism and situational patterns of severe (absence >28 days) hamstring muscle injuries in professional male and female football (soccer) players.

METHODS

The data for males were sourced from Serie A clubs participating in both national and international competitions from 2018 to 2021. For the female cohort, hamstring injuries were identified during matches of the top national/international competitions from 2017 to 2023. Video footage was obtained, and three raters categorised injury mechanisms and situational patterns. Injuries were also examined according to the month, minute and location.

RESULTS

A total of 129 severe hamstring injuries were identified, with 64 occurring in females and 65 in males. Video analysis was possible for 29 (45%) female cases and 61 (94%) male cases. Female injuries had longer lay-off times (97.8 ± 77.1 days) than males (39.6 ± 20.9 days). Females had a higher proportion of indirect contact injuries (34%) than males (13%) and a lower proportion of non-contact injuries (66% vs. 87%). Four situational patterns were identified: running was the most common for both sexes, representing 59% of female injuries and 41% of male injuries. Over-stretching injuries were split across open and CKC scenarios but collectively explained nearly half (48%) of male injuries but only one in five (21%) female injuries. Kicking injuries had a higher proportion in females (17%) than males (10%). Injuries were more common in the second half for females and the first half for males.

CONCLUSION

Females had a higher proportion of indirect contact, running and kicking injuries and a lower proportion of non-contact and stretch-type injuries than males. Understanding injury patterns can inform tailored prevention programs, considering sex-specific differences.

LEVEL OF EVIDENCE

Level IV.

Economic impact of muscle injury rate and hamstring strain injuries in professional football clubs. Evidence from LaLiga

The aims of this study were: 1) to describe the total muscular injuries, and specifically HSIs, and their corresponding missed matches; 2) to analyse their economic impact; and 3) to estimate the loss of incomes due to TV rights, in first division clubs from LaLigaTM depending on the expected and actual ranking position during the 2018/2019 season. To do that, a cross-sectional study for season 18/19 and for all players of the 20 Spanish professional football clubs was performed. The economic impact of injuries was estimated considering the missed matches and salary cost of all players and the audio-visual income loss was estimated considering the Spanish Royal Decree of Law (RDL 5/2015). The high number of muscular (270) and hamstring injuries (57) implies a high cost for professional first division football clubs, specifically € 365,811 per month for the former and € 47,388 per month for the latter. In addition, reaching a worse than expected position in LaLigaTM ranking involved a loss of 45,2 million € in TV rights incomes. The high cost of muscle injuries in first division teams justifies the need for multidisciplinary teams that are capable of reducing the number of injuries as well as recovery times.

Asymmetry in kinematics of dominant/nondominant lower limbs in central and lateral positioned college and sub-elite soccer players

Change of direction, stops, and pivots are among the most common non-contact movements associated with anterior cruciate ligament (ACL) injuries in soccer. By observing these dynamic movements, clinicians recognize abnormal kinematic patterns that contribute to ACL tears such as increased knee valgus or reduced knee flexion. Different motions and physical demands are observed across playing positions, which may result in varied lower limb kinematic patterns. In the present study, 28 college and sub-elite soccer players performed four dynamic motions (change of direction with and without ball, header, and instep kick) with the goal of examining the effect of on-field positioning, leg dominance, and gender in lower body kinematics. Motion capture software monitored joint angles in the knee, hip, and ankle. A three-way ANOVA showed significant differences in each category. Remarkably, centrally positioned players displayed significantly greater knee adduction (5° difference, p = 0.013), hip flexion (9° difference, p = 0.034), hip adduction (7° difference, p = 0.016), and dorsiflexion (12° difference, p = 0.022) when performing the instep kick in comparison to their laterally positioned counterparts. These findings suggest that central players tend to exhibit a greater range of motion when performing an instep kicking task compared to laterally positioned players. At a competitive level, this discrepancy could potentially lead to differences in lower limb muscle development among on-field positions. Accordingly, it is suggested to implement position-specific prevention programs to address these asymmetries in lower limb kinematics, which can help mitigate dangerous kinematic patterns and consequently reduce the risk of ACL injury in soccer players.

Skeletal muscle injury treatment using the Silk Elastin® injection in a rat model

Background

Skeletal muscle injury (SMI) is often treated conservatively, although it can lead to scar tissue formation, which impedes muscle function and increases muscle re-injury risk. However, effective interventions for SMIs are yet to be established.

Hypothesis

The administration of Silk Elastin® (SE), a novel artificial protein, to the SMI site can suppress scar formation and promote tissue repair.

Study design

A controlled laboratory study.

Methods

In vitro: Fibroblast migration ability was assessed using a scratch assay. SE solution was added to the culture medium, and the fibroblast migration ability was compared across different concentrations. In vivo: An SMI model was established with Sprague-Dawley rats, which were assigned to three groups based on the material injected to the SMI site: SE gel (SE group; n = 8), atelocollagen gel (Atelo group; n = 8), and phosphate buffer saline (PBS group; n = 8). Histological evaluations were performed at weeks 1 and 4 following the SMI induction. In the 1-week model, we detected the expression of transforming growth factor (TGF)-β1 in the stroma using immunohistological evaluation and real-time polymerase chain reaction analysis. In the 4-week model, we measured tibialis anterior muscle strength upon peroneal nerve stimulation as a functional assessment.

Results

In vitro: The fibroblast migration ability was suppressed by SE added at a concentration of 10⁴ μg/mL in the culture medium. In vivo: In the 1-week model, the SE group exhibited significantly lower TGFβ -1 expression than the PBS group. In the 4-week model, the SE group had a significantly larger regenerated muscle fiber diameter and smaller scar formation area ratio than the other two groups. Moreover, the SE group was superior to the other two groups in terms of regenerative muscle strength.

Conclusion

Injection of SE gel to the SMI site may inhibit tissue scarring by reducing excessive fibroblast migration, thereby enhancing tissue repair.

Clinical relevance

The findings of this study may contribute to the development of an early intervention method for SMIs.

Acute and Chronic Effects of Static Stretching on Intramuscular Hamstring Stiffness

Passive hamstring stiffness varies proximo-distally, resulting in inhomogeneous tissue strain during stretching that may affect localized adaptations and risk of muscle injuries. The purpose of the present study was to determine the acute and chronic effects of static stretching (SS) on intramuscular hamstring stiffness. Thirty healthy active participants had acute changes in passive biceps femoris (BF), semimembranosus (SM), and semitendinosus (ST) stiffness measured at 25% (proximal), 50% (middle), and 75% (distal) muscle length, using shear-wave elastography, immediately after SS. Participants then completed 4 weeks of either a SS intervention (n = 15) or no intervention (CON, n = 15) with stiffness measured before and after the interventions. The acute and chronic effects of SS were compared between anatomical regions and between regions on the basis of their relative stiffness pre-intervention. Acutely, SS decreased stiffness throughout the BF and SM (p ≤ 0.05) but not the ST (p = 0.326). However, a regional effect of stretching was observed for SM and ST with greater reduction in stiffness occurring in stiffer muscular regions (p = 0.001-0.013). Chronically, SS increased BF and ST (p < 0.05), but not SM (p = 0.422) stiffness compared with CON, but no regional effect of stretching was observed in any muscle (p = 0.361-0.833). SS resulted in contrasting acute and chronic effects, acutely decreasing stiffness in stiffer regions while chronically increasing stiffness. These results indicate that the acute effects of SS vary along the muscle's length on the basis of the relative stiffness of the muscle and that acute changes in stiffness from SS are unrelated to chronic adaptations.

Blood flow restriction therapy with exercise are no better than exercise alone in improving athletic performance, muscle strength, and hypertrophy: a systematic review and meta-analysis

BACKGROUND

The benefits of Blood Flow Restriction Therapy (BFRT) have gained attention in recent times.

OBJECTIVE

This review aimed to evaluate the immediate (up to 24 hours), intermediate (up to 6 weeks), and long term (6-10 weeks) effects of BFRT plus exercises (EX) compared to EX only on athletic performance (sprint and jump performance), muscle strength, and hypertrophy in athletes and physically active population.

METHODS

A literature search was conducted to select randomized controlled trials across four electronic databases from inception till April 2021. The search yielded twenty-seven studies in total.

RESULTS

Based on eligibility criteria, twenty-one studies were analyzed. No differences were found between both groups for immediate (standardized mean difference [SMD] -0.02, 95% confidence interval [CI] -0.31, 0.27) and long-term effects (SMD -0.30, 95%CI -0.90, 0.30) on sprint performance. For jump performance, no significant effect was observed immediately (SMD -0.02 (95% CI -1.06, 1.02) and long term (SMD -0.40 (95% CI -1.46, 0.67). Similarly, muscle torque at intermediate (SMD 0.90 (95% CI -1.01, 2.81) and long term (SMD -0.54 (95% CI -1.19, 0.12), muscle strength at intermediate (SMD 1.12 (95% CI 0.20, 2.04), and long term (SMD -0.07 (95% CI -0.56, 0.42) also showed non-significant effects. Muscle hypertrophy at intermediate (SMD 0.16 (95% CI -0.31, 0.63) and long term (SMD -0.20 (95% CI -0.90, 0.50) were not statistically significant.

CONCLUSIONS

There was no significant difference observed in BFRT plus EX group compared to the EX-group on athletic performance, muscle strength, and muscle hypertrophy.

New Anatomical Concepts regarding Pubic-Related Groin Pain: A Dissection Study

OBJECTIVE

Pubis-related groin pain remains a difficult topic in orthopedic and sports medicine. A better understanding of the anatomy of the adductors and the pubic ligaments is necessary. The aim of this study is to map all the musculotendinous attachments to the pubic ligaments and to investigate in detail all the possible inter-adductor fusions.

METHODS

The pubic symphyses were dissected in eight male and fourteen female embalmed cadavers (mean age 85 years), focusing on the fusion between the adductors, pubic ligaments, and musculotendinous attachments at the pubic ligaments. The 95% confidence intervals for the prevalence of the different conjoint tendons and tendon attachment to ligament were calculated.

RESULTS

The presence of three types of conjoint tendons was found: adductor brevis and gracilis (AB/G) 90.9 [72.2 - 97.5]%; adductor brevis and adductor longus (AB/AL) 50.0 [30.7 - 69.3]%; adductor longus and gracilis (AL/G) 50.0 [30.7 - 69.3]%. The AL, AB and G were in every cadaver attached to the anterior pubic ligament (APL). 64% of the AB and 100% of the G were attached to the inferior pubic ligament (IPL).

CONCLUSION

The proximal anatomy of the adductors is more complex than initially described. This study identified three possible conjoint tendons between the proximal adductors. The AB/G conjoint tendon was significantly more present than the AB/AL or AL/G conjoint tendon. The IPL has attachments only from the AB and G. Rectus Abdominis (RA) and AL were not attached to IPL. Mapping the musculotendinous attachments on the pubic ligaments creates more clarity on the pathophysiology of lesions in this area.

[Muscle injuries: the importance of high-resolution dynamic sonography in diagnostics, treatment and monitoring]

BACKGROUND

Muscle injuries are common in football. Imaging diagnostics have a major role in establishing a diagnosis. The main diagnostic procedures are MRI and ultrasound. Both diagnostics have advantages and disadvantages, which should be balanced against each other.

NEW ULTRASONIC TECHNIQUES

The role of MRI as the gold standard is increasingly being replaced by high-resolution ultrasound techniques, and MRI imaging is not always useful. To detect complications in the early stages it is advised to perform regular ultrasound-imaging check-ups. The healing process can be monitored, and it offers additional options for ultrasound-guided interventions such as hematoma punctures and targeted infiltrations.

ADVANTAGES AND DISADVANTAGES

However, ultrasound imaging is highly user dependent. Experienced operators can eliminate this disadvantage, which makes ultrasound a superior imaging system in many areas, especially for dynamic examinations. Nevertheless, MRI imaging remains a necessary imaging method in certain areas.

The Effect of Muscle Fatigue on the Knee Proprioception: A Systematic Review

This study aimed to systematically review and summarise the evidence about the effect of muscle fatigue on the knee proprioception of trained and non-trained individuals. A search in PubMed, Scopus, Web of Science and EBSCO databases and Google Scholar was conducted using the expression: "fatigue" AND ("proprioception" OR "position sense" OR "repositioning" OR "kinesthesia" OR "detection of passive motion" OR "force sense" OR "sense of resistance") AND "knee". Forty-two studies were included. Regarding joint-position sense, higher repositioning errors were reported after local and general protocols. Kinesthesia seems to be more affected when fatigue is induced locally, and force sense when assessed at higher target forces and after eccentric protocols. Muscle fatigue, both induced locally or generally, has a negative impact on the knee proprioception.

Epidemiology of Injury and Illness in North American Professional Men's Soccer: Comparing COVID-19 Lockdown With Previous Seasons

BACKGROUND

After COVID-19 lockdown, studies across Europe and Asia examined its effect on professional soccer injury rates and severity; however, COVID-19 lockdown influence on injuries in United States men's professional soccer has not been evaluated.

HYPOTHESIS

Injury and illness rates during the 2020 season were higher than the previous 2 seasons.

STUDY DESIGN

Retrospective observational cohort study.

LEVEL OF EVIDENCE

Level 3.

METHODS

Medical staff from participating Major League Soccer (MLS) clubs entered injuries and athletic exposures during the study period into a league-wide electronic medical record system. Injury rate and severity were analyzed to examine differentials between the 2020 COVID season and historical controls.

RESULTS

The injury incidence rate per 1000 hours in 2020 was 10.8, ie, higher than 2018 (5.4) and 2019 (5.0) (P < 0.05). Training injury incidence rate increased in 2020 (8.9) compared with 2018 (2.5) and 2019 (2.6) (P < 0.05), whereas match injury incidence decreased in 2020 (18.3) compared with 2018 (24.0) and 2019 (22.7) (P < 0.05). Incidence rates of lower extremity muscle injuries (6.04), anterior cruciate ligament (ACL) injuries (0.17), and concussions (0.49) were also higher in 2020 compared with 2018 (2.5, 0.07, 0.27) and 2019 (2.36, 0.05, 0.22) (P < 0.05). More injured players in 2020 missed >90 days (17.7%) than in 2018 (10.2%) and 2019 (10.1%) (P < 0.05). Incidence of all non-COVID-19 illness was higher in 2020 (3.93) than 2018 (1.53) and 2019 (1.32) (P < 0.05).

CONCLUSIONS

During 2020, there were significant increases in incidence rates of overall injuries, training injuries, lower extremity muscular injuries, ACL injuries, concussions, and non-COVID illness, along with a higher percentage of players missing >90 days compared with the 2 previous seasons.

CLINICAL RELEVANCE

These results may help clarify the effects of future MLS inseason work stoppages and periods of restricted training.

Influence of the External Workload on Calf Muscle Strain Injuries in Professional Football Players: A Pilot Study

BACKGROUND

The influence of external workload variables on the development of calf muscle strainsin football players has not been previously explored.

HYPOTHESIS

Overloaded players would have an increased risk of calf muscle strain injury.

STUDY DESIGN

Prospective observational study.

LEVEL OF EVIDENCE

Level 4.

METHODS

A total of 41 professional football players from 1 team were monitored for 2 consecutive seasons. Total distance covered (TD), and distances covered at high-intensity running, high sprint running, low (LACC) and high (HACC) acceleration, low (LDEC) and high (HDEC) deceleration, and at high metabolic load distance (HMLD) were monitored with GPS units. Accumulated players' external workload in the week before injury was compared with the weekly mean value of the 6 weeks before injury occurred for each player.

RESULTS

Ten players (24.3%) suffered 16 calf muscle strain injuries (3.1 injuries per 1000 hours of match play; 0.5 injuries per 1000 hours of training exposure). Players with a calf muscle injury were older (p = 0.03), with higher body weight (p = 0.01) and height (p = 0.03). Injured players displayed substantially higher total training volume (p < 0.01), TD (p < 0.01), LACC (p < 0.01), LDEC (p < 0.01), HACC (p < 0.01), HDEC (p < 0.01), and HMLD (p = 0.03) in the week before injury, in comparison with the mean values of these variables in the 6 weeks before injury.

CONCLUSION

A week with a higher-than-habitual external workload might increase the risk of calf muscle strain injury in professional football players. Calf muscle injuries were preceded by a week with unusually high workloads associated with accelerating and decelerating distances and higher training volumes.

CLINICAL RELEVANCE

Monitoring external workload indicators may be helpful in determine players with a higher risk of calf muscle strain injury due to excessive workload during training/competition.

Validity and Reliability of Handheld Dynamometry to Assess Isometric Hamstrings and Quadriceps Strength at Varying Muscle Lengths

CONTEXT

The hamstrings are the most commonly injured muscle in sports and are especially injury prone in lengthened positions. Measuring knee muscle strength in such positions could be relevant to establish injury risk. Handheld dynamometry has been shown to be a valid, reliable, and practical tool to measure isometric muscle strength clinically. The aim of this study was to assess the validity and reliability of the assessment of isometric knee muscle strength with a handheld dynamometer (HHD) at various muscle lengths, by modifying the hip and knee angles during testing.

DESIGN

Concurrent validity and test-retest reliability.

METHODS

Thirty young healthy participants were recruited. Hamstring and quadriceps isometric strength was measured with a HHD and with an isokinetic dynamometer, over 2 testing sessions, in a randomized order. Isometric strength was measured on the right lower limb in 6 different positions, with the hip at either 0° or 80° of flexion and the knee at either 30°, 60°, or 90° of flexion. Pearson and Spearman correlations were used to assess the validity, and intraclass correlation coefficients were calculated to establish the test-retest reliability of the HHD.

RESULTS

Good to excellent reliability and moderate to high validity were found in all the tested muscle length positions, except for the hamstrings in a seated position with the knee extended at 30°.

CONCLUSIONS

The use of a HHD is supported in the clinical setting to measure knee muscle strength at varying muscle lengths in healthy adults, but not for the hamstrings in a lengthened position (hip flexed and knee extended). These results will have to be confirmed in sport-specific populations.

The Role of Platelet-Rich Plasma Injection for Muscle Strains in Athletes

Muscle tears/strains are among the most common musculoskeletal injuries, posing a serious challenge for sports medicine. Aiming to reduce the time to return to play and the rate of reinjuries, apart from the traditional conservative treatments and rehabilitation protocols, new and innovative therapeutic options have emerged, particularly platelet-rich plasma (PRP). This study aims to present the available evidence regarding PRP injection for the treatment of muscle strains in athletes. Two databases were searched for articles published between January 2012 and December 2022 in Portuguese or English. The query used for the PubMed database was ("Muscles/injuries"[Mesh]) AND ("Athletes"[Mesh] OR "Athletic Injuries"[Mesh]) AND "Platelet-Rich Plasma"[Mesh], while for the Web of Science database the search was performed for "Platelet-rich plasma" AND "Muscle injuries" AND ("Athletes" OR "Athletic injuries"). Eleven studies involving athletes diagnosed with muscle injuries who received treatment with PRP injection alone, or in combination with traditional conservative treatment, compared to a control group, were included. Four randomized controlled trials, four systematic reviews/meta-analyses, two retrospective studies, and one comparative study were included. Current evidence from the highest-quality studies does not support the hypothesis of reduction of time to return to play and the rate of reinjuries after PRP injection, even though some studies reported positive results. However, the available evidence suggests that PRP might have a beneficial effect on the pain perceived by athletes following an acute muscle strain. It is challenging to arrive at definitive conclusions and translate these findings into a clinical context for treating muscle strains in athletes. The existing trials present several inconsistencies and limitations, with a heterogeneous set of patients and injuries, as well as the use of different and inconsistent methods for preparing, administering, and measuring the effects of PRP. To achieve consistent outcomes, standardizing PRP administration procedures is essential.

An in-depth study on the magnetic resonance imaging characteristics of tendon rupture in sports injuries and its correlation with patients' clinical symptoms

Muscle injuries, such as Achilles and quadriceps tendon ruptures, pose a significant challenge in elite sports, accounting for more than 30% of all sports-related injuries. Our primary goal is to investigate the MR imaging characteristics of tendon rupture in sports injuries and their relationship with patients' clinical symptoms. In our retrospective study at Zhejiang University of Traditional Chinese Medicine's Second Affiliated Hospital (Zhejiang Xinhua Hospital), we compared the clinical presentation and MRI results of 106 patients with isolated AT and QT ruptures. In the AT, the enthesis was identified as a common site of bony avulsions (30.2%). In contrast, insertional ruptures were more common in the gastrocnemius heads (69.8% and 66.0%). The low frequency of mid-substance tears (13.2% to 20.8%) demonstrated the central tendon region's inherent tensile strength. The ruptured musculotendinous junctions affected the soleus (20.8%). In QT, bony avulsions play a minor role (5.1% to 11.3%). The patella was the primary site of tears (42.2% - 45.3%), with the Vastus intermedius favoring proximal tears (58.5%). Our examination of AT and QT ruptures across sub-components sheds light on their distinct patterns and the implications for clinical practice in terms of precise diagnosis, personalized treatment, and, ultimately, better patient outcomes for these debilitating injuries.

The Future of Artificial Intelligence in Sports Medicine and Return to Play

Artificial intelligence (AI) has shown tremendous growth over the last decade, with the more recent development of clinical applications in health care. The ability of AI to synthesize large amounts of complex data automatically allows health care providers to access previously unavailable metrics and thus enhance and personalize patient care. These innovations include AI-assisted diagnostic tools, prediction models for each treatment pathway, and various tools for workflow optimization. The extension of AI into sports medicine is still early, but numerous AI-driven algorithms, devices, and research initiatives have delved into predicting and preventing athlete injury, aiding in injury assessment, optimizing recovery plans, monitoring rehabilitation progress, and predicting return to play.

Gender-specific hip strength disparities correlate with injury patterns in NCAA men's and women's soccer players

BACKGROUND

In National Collegiate Athletic Association (NCAA) soccer athletes, men have higher rates of hip and groin strains, whereas women have higher rates of knee ligament injuries. Strength imbalances of the hip and thigh, specifically in agonist-antagonist muscles, are known risk factors for these injuries.

OBJECTIVE

To perform hip and thigh strength assessments in NCAA soccer players to evaluate for differences between genders and correlations with gender-specific injury patterns.

DESIGN

With a handheld dynamometer, weight-normalized isometric strength of six muscle groups (hip abductors, hip adductors, hip flexors, hip extensors, knee flexors, knee extensors) was calculated in NCAA soccer players. The strength ratio of each agonist-antagonist muscle was also calculated (hip abductors/adductors, hip flexors/extensors, knee extensors/flexors).

PARTICIPANTS

Thirty-six NCAA soccer players (18 men, 18 women) from a single NCAA Division III institution.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Weight-normalized strength of six muscle groups and their agonist-antagonist strength ratios were compared between genders using linear mixed-effects models.

RESULTS

Compared with male players, female players had decreased weight-normalized strength for hip abduction (0.170 vs. 0.204, p = .012) and hip extension (0.172 vs. 0.211, p = .021). Otherwise, weight-normalized strength was similar between genders. When comparing agonist-antagonist strength ratios, there was a significant difference between female and male players for hip flexion:extension (1.70 vs. 1.35, p = .008), whereas the hip abduction: adduction ratio did not reach statistical significance (1.45 vs. 1.62, p = .080).

CONCLUSIONS

NCAA male and female soccer players had different hip strength profiles that fit their injury patterns. Male NCAA soccer players have higher rates of hip and groin strains, and men in the cohort had strength ratios that were deficient in the hip flexors and adductors compared with women. Female NCAA soccer players have higher rates of knee sprains and anterior cruciate ligament tears, and women in the cohort had strength ratios that were deficient in the hip abductors and extensors, which function to stabilize the knee. These strength disparities could be the focus of future gender-specific soccer injury prevention programs.

Hamstring muscle injuries in athletics

Hamstring muscle injuries (HMI) are a common and recurrent issue in the sport of athletics, particularly in sprinting and jumping disciplines. This review summarizes the latest literature on hamstring muscle injuries in athletics from a clinical perspective. The considerable heterogeneity in injury definitions and reporting methodologies among studies still needs to be addressed for greater clarity. Expert teams have recently developed evidence-based muscle injury classification systems whose application could guide clinical decision-making; however, no system has been adopted universally in clinical practice, yet.The most common risk factor for HMI is a previously sustained injury, particularly early after return-to-sport. Other modifiable (e.g. weakness of thigh muscles, high-speed running exposure) and non-modifiable (e.g. older age) risk factors have limited evidence linking them to injury. Reducing injury may be achieved through exercise-based programs, but their specific components and their practical applicability remain unclear.Post-injury management follows similar recommendations to other soft tissue injuries, with a graded progression through stages of rehabilitation to full return to training and then competition, based on symptoms and clinical signs to guide the individual speed of the recovery journey. Evidence favoring surgical repair is conflicting and limited to specific injury sub-types (e.g. proximal avulsions). Further research is needed on specific rehabilitation components and progression criteria, where more individualized approaches could address the high rates of recurrent HMI. Prognostically, a combination of physical examination and magnetic resonance imaging (MRI) seems superior to imaging alone when predicting 'recovery duration,' particularly at the individual level.

Changes in hamstring contractile properties during the competitive season in young football players

Background

The study aimed to examine alterations and imbalances in hamstring muscle contractile properties among young football players throughout their competitive season, and to understand how these changes might contribute to the risk of muscle injuries. Hamstring injuries are particularly common in football, yet the underlying causes and effective prevention methods remain unclear.

Methods

The research involved 74 young footballers who were assessed before the season (pre-test) and after 12 weeks of training (post-test). To evaluate changes in hamstring muscle contractile properties, specifically the left and right biceps femoris (BF) and semitendinosus (ST), tensiomyography (TMG) parameters were utilized.

Results

In comparison to the BF muscle, significant differences in time delay (Td) between the left and right sides in the post-test (p = 0.0193), and maximal displacement (Dm) between the left and right sides at the pre-test (p = 0.0395). However, significant differences in Dm were observed only in the left ST muscle between the pre- and post-tests (p = 0.0081). Regarding lateral symmetry, BF registered measurements of 79.7 ± 13.43 (pre-test) and 77.4 ± 14.82 (post-test), whereas ST showed measurements of 87.0 ± 9.79 (pre-test) and 87.5 ± 9.60 (post-test).

Conclusions

These assessments provided TMG reference data for hamstring muscles in young footballers, both before the season and after 12 weeks of in-season training. The observed changes in the contractile properties and decrease in lateral symmetry of the BF in both tests suggest an increased risk of injury.

Development and validation of an interview guide for examining the effects of sports careers on the quality of life of retired Portuguese football players

Introduction

Considering the importance of assessing the impacts resulting from a sport career, this study aimed at developing and validating a semi-structure interview guide suitable for quantifying the sociodemographic and epidemiological profile of former professional football players.

Methods

Based on the theoretical frameworks and several methodological procedures, an interview guide was developed, consisting of 3 areas of conceptual organization (A1. Biographical data; A2. Professional Career; and A3. Post-Career Transition) and 8 data collection categories (C1. Personal data; C2. Professional data; C3. Sociodemographic background; C4. Epidemiological pathway; C5. Moment of career retirement (career transition); C6. Post-career sociodemographic pathway; C7. Post-career epidemiological pathway; and C8. Perceptions of post-career planning). Thus, in procedural terms, four stages were considered for the construction and validation of the interview guide, namely the Ad hoc construction of the interview guide (i), the review of the in-terview guide by a panel of experts (ii), definition of procedures and protocol for the application of the interview (iii), and the application of the pilot study for the face validation of the interview guide (iv). The sample consisted of two former Portuguese professional players.

Results and discussion

To analyze and discuss the data, a content analysis was carried out on all the answers given to each question in the script by the interviewees. From them, matrices were created with the response references to each subcategory. In this way, it was possible to analyse the type of answers given by the interviewees and relate them to the theoretical perspectives of the topic being investigated. The results showed that the interview guide for the study of the impacts of the sports careers on the quality of life of Portuguese former football players shows reliability for the collection of qualitative and quantitative information from the respective content analysis. The use of the interview guide characterizes the path of former player, providing information and knowledge on the sociodemographic and epidemiological impact factors resulting from their post-career.

Association Between Total Genotype Score and Muscle Injuries in Top-Level Football Players: a Pilot Study

BACKGROUND

Recently, genetic predisposition to injury has become a popular area of research and the association between a few single nucleotide polymorphisms (SNPs) and the susceptibility to develop musculoskeletal injuries has been shown. This pilot study aimed to investigate the combined effect of common gene polymorphisms previously associated with muscle injuries in Italian soccer players.

RESULTS

A total of 64 Italian male top football players (age 23.1 ± 5.5 years; stature 180.2 ± 7.4 cm; weight 73.0 ± 7.9 kg) were genotyped for four gene polymorphisms [ACE I/D (rs4341), ACTN3 c.1729C > T (rs1815739), COL5A1 C > T (rs2722) and MCT1 c.1470A > T (rs1049434)]. Muscle injuries were gathered for 10 years (2009-2019). Buccal swabs were used to obtain genomic DNA, and the PCR method was used to genotype the samples. The combined influence of the four polymorphisms studied was calculated using a total genotype score (TGS: from 0 to 100 arbitrary units; a.u.). A genotype score (GS) of 2 was assigned to the "protective" genotype for injuries, a GS of 1 was assigned to the heterozygous genotype while a GS of 0 was assigned to the "worst" genotype. The distribution of genotype frequencies in the ACE I/D (rs4341), ACTN3 c.1729C > T (rs1815739) and MCT1 c.1470A > T (rs1049434) polymorphisms was different between non-injured and injured football players (p = 0.001; p = 0.016 and p = 0.005, respectively). The incidence of muscle injuries was significantly different among the ACE I/D (rs4341), ACTN3 c.1729C > T (rs1815739) and COL5A1 C > T (rs2722) genotype groups, showing a lower incidence of injuries in the "protective" genotype than "worse" genotype (ACE, p < 0.001; ACTN3, p = 0.005) or intermediate genotype (COL5A1, p = 0.029). The mean TGS in non-injured football players (63.7 ± 13.0 a.u.) was different from that of injured football players (42.5 ± 12.5 a.u., p < 0.001). There was a TGS cut-off point (56.2 a.u.) to discriminate non-injured from injured football players. Players with a TGS beyond this cut-off had an odds ratio of 3.5 (95%CI 1.8-6.8; p < 0.001) to suffer an injury when compared with players with lower TGS.

CONCLUSIONS

These preliminary data suggest that carrying a high number of "protective" gene variants could influence an individual's susceptibility to developing muscle injuries in football. Adapting the training load parameters to the athletes' genetic profile represents today the new frontier of the methodology of training.

Relationship Between Postural Stability and Proprioception, Pain, Quadriceps Strength, and Muscle Tightness in Athletes With Patellar Tendinopathy

BACKGROUND

Athletes with patellar tendinopathy (PT) have postural stability deficits; however, the underlying mechanisms and factors responsible remain unknown. The effect on postural stability in PT of decreased quadriceps strength, altered proprioception, lower-limb muscle tightness, and knee pain, which explain postural stability deficiency in other populations, is uninvestigated.

HYPOTHESIS

Proprioceptive acuity, muscle tightness, quadriceps strength, and pain predict postural stability in athletes with PT.

STUDY DESIGN

Cross-sectional comparative study.

LEVEL OF EVIDENCE

Level 2.

METHODS

A total of 43 athletes with PT and 43 healthy athletes were enrolled. Static and dynamic postural stability, proprioceptive acuity, muscle tightness, quadriceps strength, and pain were evaluated using a force platform, Y-balance test (YBT), a weight discrimination protocol, a goniometer, an isometric dynamometer, and a valid questionnaire, respectively.

RESULTS

Athletes with PT had significantly worse static and dynamic postural stability in the affected limb (AL) compared with the nonaffected limb (NAL) (P < 0.01) and the control group (P < 0.01). Athletes suffering from PT revealed lower quadriceps strength (P < 0.01), proprioceptive acuity (P = 0.02), and higher muscle tightness in the AL compared with the NAL and controls. Quadriceps weakness of the AL and pain in athletes with PT explained the variance of dynamic postural stability impairment.

CONCLUSION

Athletes with PT have postural stability deficiency compared with healthy peers. Our results demonstrate that quadriceps muscle weakness and pain are the factors that explain postural stability impairment.

CLINICAL RELEVANCE

These results can assist clinicians in the design of therapeutic balance rehabilitation programs by acting not only on pain relief but also on quadriceps strengthening through resistance training to avoid subsequent injuries in athletes with PT.