The effect of hamstring flexibility on peak hamstring muscle strain in sprinting

Technical Sprinting in the Early Phase of Hamstring Injury Rehabilitation to Accelerate Return to Full Participation in Track and Field Athletes: A Comparative Study of Two Rehabilitation Strategies

INTRODUCTION

Hamstring injuries are common in track and field athletes with a higher incidence in males than females. It causes a significant loss in training time and a decline in performance. This study evaluated rehabilitation strategies to accelerate return to full participation following hamstring injury.

METHODS

Thirty-three athletes (22 males; 11 females) were screened from November 2021 to October 2023 until their final major competition. Out of these, 17 athletes with hamstring injuries were included in this study which were further divided into two groups, A (n=8) and B (n=9), using stratified random sampling with single blinding. Group A received technical sprints using mini hurdles as part of their training from the early stages of rehabilitation, while Group B underwent high-volume low-intensity rehabilitation before progressing to sprints. The progress of each group was monitored on a weekly basis. The average time loss was calculated using Microsoft Excel (Microsoft® Corp., Redmond, WA) and Google Forms (Google, Inc., Mountain View, CA) with built-in validation.

RESULTS

 The two groups demonstrated a significant difference in recovery times. In group A, the length of hamstring tenderness (LHT) improved from 9 ± 2.7 (95% CI 2.27) to 0.15 ± 0.3 (95% CI 0.62), active total knee extension (ATKE) from 161.8 ± 7.1 (95% CI 5.95) to 175.4 ± 2 (95% CI 2.3), and Numeric Pain Rating Scale (NPRS) in the isometric test from 5.6 ± 1.09 (95% CI 0.88) to 0.6 ± 0.5 (95% CI 0.63) with p<0.05, and in Group B, LHT improved from 6.8 ± 2.1 (95% CI 1.62) to 0.6 ± 0.7 (95% CI 0.55), ATKE improved from 168.7 ± 8.2 (95% CI 6.3) to 178.7 ± 2.7 (95% CI 2.06) and NPRS with resisted isometric test improved from 6 ± 1.4 (95% CI 1.08) to 0.8 ± 0.7 (95% CI 0.51) with p<0.05. However, Group A took an average of 3.55 weeks (1.22 SD 95% CI 1.08) and Group B took an average of 4.53 weeks (1.98 SD, 95% CI 1.52) to resume full participation. Three athletes from Group A and six athletes from Group B experienced hamstring tightness during the competition, two athletes from Group B were forced to withdraw from the competition due to hamstring reinjury.

CONCLUSIONS

The findings indicate that an early technical sprint program can facilitate an early return to full participation. This research can be a guide toward accelerated and integrated hamstring injury rehabilitation among track and field athletes.

Risk factors for hamstring strain injury in male college American football players -a preliminary prospective cohort study

BACKGROUND

Given the frequency of hamstring strain injuries (HSI) among male college American football players, several studies have attempted to determine whether certain risk factors can predict their occurrence. However, no consensus on modifiable risk factors for HSIs in male college American football players has yet been reached to prevent these injuries. This study aimed to clarify risk factors for HSI prospectively in college male American football players.

METHODS

A total of 78 male college American football players, whose positions were limited to skill positions, were medically assessed for potential risk factors of HSI. The preseason medical assessment included anthropometric measurements, joint laxity and flexibility, muscle flexibility, muscle strength, and balance ability.

RESULTS

HSI occurred in a total of 25 thighs from 25 players (32.1%). Injured players had significantly lower hamstring flexibility (p = 0.02) and hamstring to quadriceps strength ratio (H/Q) (p = 0.047) compared to uninjured players. Additionally, injured players had significantly lower general joint laxity scores, especially for the total (p = 0.04), hip (p = 0.007), and elbow (p = 0.04) scores, compared to uninjured players.

CONCLUSIONS

Lower hamstring flexibility, lower hamstring to quadriceps strength ratio, and lower general joint laxity score were identified as risk factors for HSI in male college American football players placed in skill positions. The muscle flexibility and H/Q ratio could be useful in preventing HSI in such players.

London International Consensus and Delphi study on hamstring injuries part 3: rehabilitation, running and return to sport

Hamstring injuries (HSIs) are the most common athletic injury in running and pivoting sports, but despite large amounts of research, injury rates have not declined in the last 2 decades. HSI often recur and many areas are lacking evidence and guidance for optimal rehabilitation. This study aimed to develop an international expert consensus for the management of HSI. A modified Delphi methodology and consensus process was used with an international expert panel, involving two rounds of online questionnaires and an intermediate round involving a consensus meeting. The initial information gathering round questionnaire was sent to 46 international experts, which comprised open-ended questions covering decision-making domains in HSI. Thematic analysis of responses outlined key domains, which were evaluated by a smaller international subgroup (n=15), comprising clinical academic sports medicine physicians, physiotherapists and orthopaedic surgeons in a consensus meeting. After group discussion around each domain, a series of consensus statements were prepared, debated and refined. A round 2 questionnaire was sent to 112 international hamstring experts to vote on these statements and determine level of agreement. Consensus threshold was set a priori at 70%. Expert response rates were 35/46 (76%) (first round), 15/35 (attendees/invitees to meeting day) and 99/112 (88.2%) for final survey round. Statements on rehabilitation reaching consensus centred around: exercise selection and dosage (78.8%-96.3% agreement), impact of the kinetic chain (95%), criteria to progress exercise (73%-92.7%), running and sprinting (83%-100%) in rehabilitation and criteria for return to sport (RTS) (78.3%-98.3%). Benchmarks for flexibility (40%) and strength (66.1%) and adjuncts to rehabilitation (68.9%) did not reach agreement. This consensus panel recommends individualised rehabilitation based on the athlete, sporting demands, involved muscle(s) and injury type and severity (89.8%). Early-stage rehab should avoid high strain loads and rates. Loading is important but with less consensus on optimum progression and dosage. This panel recommends rehabilitation progress based on capacity and symptoms, with pain thresholds dependent on activity, except pain-free criteria supported for sprinting (85.5%). Experts focus on the demands and capacity required for match play when deciding the rehabilitation end goal and timing of RTS (89.8%). The expert panellists in this study followed evidence on aspects of rehabilitation after HSI, suggesting rehabilitation prescription should be individualised, but clarified areas where evidence was lacking. Additional research is required to determine the optimal load dose, timing and criteria for HSI rehabilitation and the monitoring and testing metrics to determine safe rapid progression in rehabilitation and safe RTS. Further research would benefit optimising: prescription of running and sprinting, the application of adjuncts in rehabilitation and treatment of kinetic chain HSI factors.

Effects of changes in optimal muscle fibre length in the biceps femoris long head on muscle force during the late swing phase of maximal speed sprinting: a simulation study

Hamstring strain injuries would frequently occur during the late swing phase of sprinting, while increasing biceps femoris long head's (BFlh) fascicle length induced by eccentric contraction exercises can reduce the risk of strain injuries. Thus, using a musculoskeletal modelling simulation, we examined how manipulating BFlh optimal muscle fibre length would change muscle force during the late swing phase of sprinting for providing knowledge preventing hamstring strain injuries. A motion capture system was used to collect kinematic data from 40 male athletes during maximal speed sprinting. Muscle force and force-generating capabilities determined by force-length-velocity properties were estimated with three BFlh optimal muscle fibre lengths (90%, 110% and 120%), which were perturbed from the nominal (100%). During the late swing phase of sprinting, the muscle force and force-generating capabilities, induced by the force-length property rather than the force-velocity property, were increased by increases in BFlh optimal muscle fibre length. Moreover, magnitudes of the simulated increases in muscle force and force-generating capabilities were correlated with the peak BFlh muscle-tendon unit length. These results demonstrate that lengthening BFlh optimal muscle fibre might increase muscle force during the late swing phase, and the magnitude of increment would be associated with increasing muscle-tendon unit length.

The Role of Structured Foam Rolling Programs in Improving Hamstring Flexibility: A Critically Appraised Topic

Focused Clinical Question: What is the efficacy of structured foam rolling protocols at increasing hamstring muscle flexibility in active adults when compared with just maintaining regular levels of activity? Clinical Bottom Line: There is significant evidence to support the use of structured foam rolling programs in active adults to improve hamstring flexibility.

Effect of sciatic nerve mobilisation on muscle flexibility among diabetic and non-diabetic sedentary individuals: a comparative study

The purpose of the present study was to compare the effect of sciatic nerve mobilisation on muscle flexibility among diabetic and non-diabetic sedentary individuals. The study was a pre-post experimental-group design. A sample of 40 sedentary subjects was assigned into two groups; Group A (diabetics: 10 males and 10 females) and Group B (non-diabetics: 10 males and 10 females). Both groups were tested for hamstring and calf flexibility following which sciatic nerve mobilisation was given to the most affected lower limb in terms of reduced hamstring and calf flexibility. Hamstring flexibility was checked by active knee extension test and calf flexibility was checked with the distance-to-wall technique using a tape measure. It was a two-week program in which subjects were given sciatic nerve mobilisation using sliders technique after which flexibility was checked. Three sessions per week were given for two weeks and muscle flexibility of hamstring and calf was measured after the intervention. The present study findings reveal that sciatic nerve mobilisation by sliders technique when given to diabetic and non-diabetic groups of sedentary individuals for two weeks, enhance patient outcomes in both the groups in terms of increase in hamstring and calf flexibility, but results were more significant in non-diabetic individuals as compared to diabetic individuals. In conclusion, sciatic nerve mobilisation resulted in an increase of muscle flexibility of hamstring and calf muscles in both groups.

Effects of flexibility and strength training on peak hamstring musculotendinous strains during sprinting

BACKGROUND

Hamstring injury is one of the most common injuries in sports involving sprinting. Hamstring flexibility and strength are often considered to be modifiable risk factors in hamstring injury. Understanding the effects of hamstring flexibility or strength training on the biomechanics of the hamstring muscles during sprinting could assist in improving prevention strategies and rehabilitation related to these injuries. The purpose of this study was to determine the effects of altering hamstring flexibility or strength on peak hamstring musculotendinous strain during sprinting.

METHODS

A total of 20 male college students (aged 18-24 years) participated and were randomly assigned to either a flexibility intervention group or a strength intervention group. Each participant executed exercise training 3 times a week for 8 weeks. Flexibility, sprinting, and isokinetic strength testing were performed before and after the 2 interventions. Paired t tests were performed to determine hamstring flexibility or strength intervention effects on optimal hamstring musculotendinous lengths and peak hamstring musculotendinous strains during sprinting.

RESULTS

Participants in the flexibility intervention group significantly increased the optimal musculotendinous lengths of the semimembranosus and biceps long head (p ≤ 0.026) and decreased peak musculotendinous strains in all 3 bi-articulate hamstring muscles (p ≤ 0.004). Participants in the strength-intervention group significantly increased the optimal musculotendinous lengths of all 3 hamstring muscles (p ≤ 0.041) and significantly decreased their peak musculotendinous strain during sprinting (p ≤ 0.017).

CONCLUSION

Increasing hamstring flexibility or strength through exercise training may assist in reducing the risk of hamstring injury during sprinting for recreational male athletes.

Immediate effects of a direct myofascial release technique on hip and cervical flexibility in inactive females with hamstring shortening: A randomized controlled trial

BACKGROUND

Currently, greater background is required about the effectiveness of myofascial release (MFR) on muscle flexibility.

OBJECTIVE

Our goal was to determine the immediate effect of a direct MFR technique on hip and cervical flexibility in inactive females with hamstring shortening.

METHOD

The sample group included 68 female university students, randomly divided into a control group (n = 34) and an experimental group (n = 34). A placebo technique was used with the control group, and direct MFR on the posterior thigh region was used with the experimental group.

RESULTS

The mixed factorial ANOVA did not show significant intergroup differences (p > 0.05). In the experimental group, Bonferroni post hoc test showed significant intragroup differences between pre-test and post-test 1, as well as between pre-test and post-test 2 for the three ischiotibial muscle flexibility tests (p < 0.001). Cervical flexion range of motion showed significant differences between pre-test and post-test 1 (p < 0.001).

CONCLUSIONS

We conclude that the protocol based on a single direct MFR intervention was no more effective than the placebo in improving flexibility both locally at the hamstring level and remotely at the level of the cervical extensor muscles. Future research should consider different MFR techniques on the immediate increase in muscle flexibility and the long-term effect of MFR, as well as consider different intervention groups.

The mechanism of hamstring injuries - a systematic review

Background

Injuries to the hamstring muscles are among the most common in sports and account for significant time loss. Despite being so common, the injury mechanism of hamstring injuries remains to be determined.

Purpose

To investigate the hamstring injury mechanism by conducting a systematic review.

Study design

A systematic review following the PRISMA statement.

Methods

A systematic search was conducted using PubMed, EMBASE and the Cochrane Library. Studies 1) written in English and 2) deciding on the mechanism of hamstring injury were eligible for inclusion. Literature reviews, systematic reviews, meta-analyses, conference abstracts, book chapters and editorials were excluded, as well as studies where the full text could not be obtained.

Results

Twenty-six of 2372 screened original studies were included and stratified to the mechanism or methods used to determine hamstring injury: stretch-related injuries, kinematic analysis, electromyography-based kinematic analysis and strength-related injuries. All studies that reported the stretch-type injury mechanism concluded that injury occurs due to extensive hip flexion with a hyperextended knee. The vast majority of studies on injuries during running proposed that these injuries occur during the late swing phase of the running gait cycle.

Conclusion

A stretch-type injury to the hamstrings is caused by extensive hip flexion with an extended knee. Hamstring injuries during sprinting are most likely to occur due to excessive muscle strain caused by eccentric contraction during the late swing phase of the running gait cycle.

Level of evidence

Level IV

Individual Region- and Muscle-specific Hamstring Activity at Different Running Speeds

INTRODUCTION

Hamstring strain injuries typically occur in the proximal biceps femoris long head (BFlh) at high running speeds. Strain magnitude seems to be the primary determinant of strain injury, and may be regulated by muscle activation. In running, BFlh strain is largest in the proximal region, especially at high speeds. However, region-specific activity has not been examined. This study examined the proximal-distal and intermuscular activity of BFlh and semitendinosus (ST) as a function of increasing running speed.

METHODS

Thirteen participants ran at steady speeds of 4.1 (slow), 5.4 (moderate), and 6.8 m·s (fast) on a treadmill. Region- and muscle-specific EMG activity were recorded at each speed using high-density EMG, and were normalized to maximal voluntary isometric activity. Muscle-tendon unit lengths were calculated from kinematic recordings. Speed effects, regional, and intermuscular differences were tested with Statistical Parametric Mapping.

RESULTS

With increasing running speed, EMG activity increased in all regions of both muscles to a similar extent in the clinically relevant late swing phase. Increases in muscle-tendon unit lengths in late swing as a function of running speed were comparatively small. In fast running, EMG activity was highest in late swing in all regions, and reached 115% ± 20% (proximal region, mean ± 95% confidence limit), 106% ± 11% (middle), and 124% ± 16% (distal) relative to maximal voluntary isometric activity in BFlh. Regional and intermuscular EMG patterns were highly individual, but each individual maintained similar proximal-distal and intermuscular EMG activity patterns across running speeds.

CONCLUSIONS

Running is associated with highly individual hamstring activity patterns, but these patterns are similar across speeds. It may thus be crucial to implement running at submaximal speeds early after hamstring injury for restoration of normal neuromuscular function.

The immediate effect of IASTM vs. Vibration vs. Light Hand Massage on knee angle repositioning accuracy and hamstrings flexibility: A pilot study

INTRODUCTION

The effectiveness of novel soft-tissue interventions relative to traditional ones requires further exploration. The purpose of this pilot study was to evaluate the immediate effect of Instrument Assisted Soft Tissue Mobilization (IASTM) compared to Vibration Massage or Light Hand Massage on hamstrings' flexibility and knee proprioception.

METHODS

16 healthy non-injured male participants (mean age 23.7 years, height 1.80 cms and body mass 77.7 kg) were randomly assigned to the following interventions: (a) 5min IASTM, (b) 5min Vibration Massage and (c) 8min Light Hand-Massage, sequentially delivered to all participants with an in-between 1-week time interval. A single application of each intervention was given over the hamstrings of their dominant leg (repeated measures under 3 different experimental conditions). An active knee angle reproduction proprioception test and the back-saver sit and reach flexibility test were performed before and immediately after each intervention. Reliability of outcomes was also assessed.

RESULTS

Reliability for flexibility (ICC_3,1 = 0.97-0.99/SEM = 0.83-1.52 cm) and proprioception (ICC_3,1 = 0.83-0.88/SEM = 1.63-2.02°) was very good. For flexibility, statistically significant immediate improvement (p < 0.001) was noted in all 3 groups (1.61-3.23 cm), with no between-group differences. For proprioception, improvement in the IASTM (2.12°), Vibration Massage (0.32°) and Light Hand-Massage (1.17°) conditions was not statistically significant; no between-group differences were also evident.

CONCLUSIONS

Our findings indicate that muscle flexibility was positively influenced immediately after a single intervention of IASTM, Vibration Massage or Light Hand Massage. Proprioception changes were not statistically significant either within or between groups. Further evaluation of those interventions in a larger population with hamstrings pathology is required.

Hamstring muscle-tendon unit lengthening and activation in instep and cut-off kicking

Hamstring muscle strain injury is one of the most common injuries in sports involving sprinting and kicking. Studies examining hamstring kinematics and activations are rich for sprinting but lacking for kicking. The purpose of this study was to examine kinematics and activations of hamstring muscles in instep and cut-off kicking tasks frequently performed in soccer. Videographic and electromyographic (EMG) data were collected for 11 male soccer-majored college students performing the two kicking tasks. Peak hamstring muscle-tendon unit lengths, elongation velocities, and maximum linear envelop EMG data were identified and compared among hamstring muscles and between kicking tasks. Hamstring muscles exhibited activated elongations before and after the contact of the kicking foot with the ball. The muscle-tendon unit lengths peaked in the follow-through phase. The peak elongation velocity of the semimembranosus was significantly greater than that of the semitendinosus and biceps femoris (p = 0.001). The maximum linear envelop EMG of the biceps femoris was significantly greater than that of the semimembranosus (p = 0.026). The potential for hamstring injury exists in the follow-through phase of each kicking task. The increased hamstring muscle-tendon unit elongation velocities in kicking tasks may explain the more severe hamstring injuries in kicking compared to sprinting.

Effects of flexibility and strength interventions on optimal lengths of hamstring muscle-tendon units

OBJECTIVES

The aim of the present study was to determine the effects of altering both hamstring flexibility and strength on hamstring optimal lengths.

DESIGN

Controlled laboratory study.

METHODS

A total of 20 male and 20 female college students (aged 18-24 years) participated in this study and were randomly assigned to either a flexibility intervention group or a strength intervention group. Passive straight leg raise and isokinetic strength test were performed before and after interventions. Paired T-tests were performed to determine hamstring flexibility or strength intervention effects on hamstring optimal lengths.

RESULTS

Male participants in the flexibility intervention group significantly increased range of hip joint flexion (P=0.001) and optimal lengths of semimembranosus and biceps long head (P≤0.026). Male participants in the strength intervention group significantly increased hamstring strength (P=0.001), the range of hip joint flexion (P=0.037), and optimal lengths of all three bi-articulated hamstring muscles (P≤0.041). However, female participants did not significantly increase their hamstring optimal lengths in either intervention groups (P≥0.097) although both groups significantly increased the range of hip joint flexion and strength (P≤0.009).

CONCLUSION

Hamstring optimal lengths can be modified through flexibility intervention as well as strength intervention for male participants, but not for female participants in this study. Hamstring optimal lengths should be considered as hamstring flexibility measures in future prospective studies to identify potentially modifiable risk factors for hamstring injury.

Is Poor Hamstring Flexibility a Risk Factor for Hamstring Injury in Gaelic Games?

Context:Hamstring injuries are a leading cause of injury in Gaelic games. Hamstring flexibility as a risk factor for hamstring injury has not yet been examined prospectively in Gaelic games.Objective:To examine whether hamstring flexibility, using the modified active knee extension (AKE) test, and previous injury are risk factors for hamstring injury in Gaelic players and to generate population-specific AKE cutoff points.Design:Prospective cohort study.Setting:School and colleges.Patients (or Other Participants):Adolescent and collegiate Gaelic footballers and hurlers (n = 570).Intervention(s):The modified AKE test was completed at preseason, and hamstring injuries were assessed over the course of one season. Any previous hamstring injuries were noted in those who presented with a hamstring injury.Main Outcome Measures:Bilateral AKE scores and between-leg asymmetries were recorded. Receiver operating characteristic curves were implemented to generate cutoff points specific to Gaelic players. Univariate and backward stepwise logistic regression analyses were completed to predict hamstring injuries, hamstring injuries on the dominant leg, and hamstring injuries on the nondominant leg.Results:Mean flexibility of 64.2° (12.3°) and 64.1° (12.4°) was noted on the dominant and nondominant leg, respectively. Receiver operating characteristic curves generated a cutoff point of < 65° in the AKE on the nondominant leg only. When controlled for age, AKE on the nondominant leg was the only predictor variable left in the multivariate model (odds ratio = 1.03) and significantly predicted hamstring injury (χ2 = 9.20,P = .01). However, the sensitivity was 0% and predicted the same amount of cases as the null model. It was not possible to generate a significant model for hamstring injuries on the dominant leg (P > .05), and no variables generated aPvalue < .20 in the univariate analysis on the nondominant leg.Conclusions:Poor flexibility noted in the AKE test during preseason screening and previous injury were unable to predict those at risk of sustaining a hamstring strain in Gaelic games with adequate sensitivity.

Effect of Pre-training and Post-training Nordic Exercise on Hamstring Injury Prevention, Recurrence, and Severity in Soccer Players

Objective

To investigate the effect of adding Nordic exercise as post-training in decreasing hamstring initial, recurrent injuries rates, and their severity.

Methods

In this randomly controlled trial study, 34 professional football players aged 21 to 35 years were randomly assigned into two groups (17 players each) from Sporting clubs at Alexandria, Egypt. For group one, Nordic hamstring exercise (NHE) was performed pre-training and post-training. For group two, NHE was only performed pre-training. The control group was the same team during the previous season. Length of the trial was 12 weeks. The Australian football association injury form was used to collect incidence of injuries for each subject in both groups.

Results

Pooled results based on total injuries showed that group one had significantly less hamstring initial injuries (92% less) than the previous season, while group two had 80% less initial injuries and 85% less recurrent injuries than previous season. Regarding the severity of injuries in term of mean number of absent days, it was 1 day for group one and 2.7 days for group two while it was 7.95 days for the previous season during total risk time of 116.3±13.2 and 117.6±5.7 exposure hours for group one and group two, respectively.

Conclusion

The use of NHE as a prevention protocol was effective in reducing all hamstring injuries with the use of NHE during pre-training and post-training having the greatest effect.

Changes Over a Decade in Anthropometry and Fitness of Elite Austrian Youth Soccer Players

Increases in physical (e.g., high-intensity running and sprinting), technical (e.g., passing rate), and tactical (e.g., player density) aspects made elite level soccer more challenging within the past years. The aim of the study was to evaluate whether these evolutions are also been reflected in changes in anthropometric and fitness characteristics between former (2002 to 2005) and current (2012 to 2015) elite Austrian youth development center (U13 to U14) and soccer academy (U15 to U18) players. A battery of anthropometric, general and soccer-specific fitness tests was conducted annually at the end of each year. Independent t-test and Cohen’s d (ES) were calculated to compare the two four-year periods (2530 vs. 2611 players) at each age group separately. Current players were significantly faster in 20 m sprint (ES = 0.26–0.50) and reaction test (ES = 0.15–0.39, except for U18), but less flexible at sit-and-reach (ES = –0.19 to –0.55), in all age categories. Whereas height (ES = 0.26–0.32), body mass (ES = 0.11–0.18) and countermovement jump (ES = 0.24–0.26) increased significantly at youth development center level, current academy players performed superior at shuttle sprint (ES = 0.21–0.59), hurdles agility run (ES = 0.24–0.49), and endurance run (ES = 0.11–0.20). These changes over time in speed, change-of-direction ability, lower-body power, coordination, and endurance were attributed to modern training approaches (e.g., modified games and change-of-direction drills) and modifications in selection politics (e.g., coaches favor speed and decision-making skills).