Altering the Length-Tension Relationship with Eccentric Exercise

Multilevel Models for the Analysis of Angle-Specific Torque Curves with Application to Master Athletes

The aim of this paper was to outline a multilevel modeling approach to fit individual angle-specific torque curves describing concentric knee extension and flexion isokinetic muscular actions in Master athletes. The potential of the analytical approach to examine between individual differences across the angle-specific torque curves was illustrated including between-individuals variation due to gender differences at a higher level. Torques in concentric muscular actions of knee extension and knee extension at 60º·s⁻¹ were considered within a range of motion between 5º and 85º (only torques “truly” isokinetic). Multilevel time series models with autoregressive covariance structures with standard multilevel models were superior fits compared with standard multilevel models for repeated measures to fit angle-specific torque curves. Third and fourth order polynomial models were the best fits to describe angle-specific torque curves of isokinetic knee flexion and extension concentric actions, respectively. The fixed exponents allow interpretations for initial acceleration, the angle at peak torque and the decrement of torque after peak torque. Also, the multilevel models were flexible to illustrate the influence of gender differences on the shape of torque throughout the range of motion and in the shape of the curves. The presented multilevel regression models may afford a general framework to examine angle-specific moment curves by isokinetic dynamometry, and add to the understanding mechanisms of strength development, particularly the force-length relationship, both related to performance and injury prevention.

The efficacy of exercise in preventing injury in adult male football: a systematic review of randomised controlled trials

BACKGROUND

Injury prevention measures might reduce the impact of injury on footballers and football clubs. Increasing research has evaluated the use of exercise for injury prevention. However, research has focused on adolescent females. No high-quality systematic reviews have evaluated the efficacy of all forms of exercise on preventing injury in adult male football.

OBJECTIVE

Our objective was to conduct a systematic review to evaluate the efficacy of exercise in preventing injury in adult male football.

DATA SOURCES

Comprehensive searches of electronic databases CINAHL (Cumulative Index to Nursing and Allied Health Literature), MEDLINE, Embase, AMED (The Allied and Complementary Medicine Database), the Cochrane Central Register of Controlled Trials, PEDro (The Physiotherapy Evidence Database), SPORTDiscus™, the National Research Register, Current Controlled Trials website (York), and http://www.ClinicalTrials.gov were conducted using predefined search terms to identify relevant studies published up to 1 March 2013. Screening of references, searches of grey literature, and hand searches of relevant journals were also employed.

STUDY SELECTION

Included studies were randomized controlled trials using injury incidence as an outcome measure to evaluate the efficacy of an exercise intervention on uninjured male footballers aged 16 years and over. Articles not written in English were excluded.

DATA EXTRACTION

Two researchers independently searched data sources, screened studies for eligibility, evaluated risk of bias, and extracted data using predefined criteria.

STUDY APPRAISAL AND SYNTHESIS METHODS

Risk of bias of included trials was assessed using the Cochrane Collaboration's tool for assessing risk of bias. There was insufficient trial comparability (outcome measures, interventions, injury type) for meta-analysis, and a qualitative analysis was performed.

RESULTS

Eight trials (n = 3,355) from five countries met the inclusion criteria. All trials were assessed as having a high risk of bias. Two trials reported statistically significant reductions in hamstring injuries with eccentric exercise, and two reported statistically significant reductions in recurrent ankle sprains with proprioceptive exercise. Four trials showed no statistically significant difference in injury incidence with exercise interventions targeting a range of injuries.

LIMITATIONS

Notable limitations of included trials included poor reporting and limited blinding. A high risk of bias and insufficient comparability across trials prevented quantitative data synthesis.

CONCLUSIONS

Limitations in the context of study quality and heterogeneity resulted in an inability to reach a clear conclusion regarding efficacy of exercise for injury prevention in adult male football. Future low risk of bias, properly powered, and comprehensively reported trials are warranted to evaluate the efficacy of exercise on injury prevention. The use of eccentric hamstring exercise for hamstring injury prevention and proprioceptive training for recurrent ankle sprain prevention might be a good focus for future trials, as existing trials with a high risk of bias suggest an effect.

Large eccentric strength increase using the Copenhagen Adduction exercise in football: A randomized controlled trial

Hip adductor injuries are frequent in football, and players with low adductor strength appear to be at increased risk of injury. High adductor muscle activity has been shown in the Copenhagen Adduction exercise (CA); however, an associated strength gain has not been investigated. This study aims to examine the eccentric hip adduction strength (EHAD) gain using the CA in-season. Two U-19 sub-elite football teams, including 24 football players, were randomized to either an 8-week supervised progressive training program in addition to the usual training (intervention) or to continue training as usual (control). EHAD, eccentric hip abduction strength (EHAB), and side-bridge endurance were measured using reliable test procedures at baseline and follow-up by a blinded tester. There was a significant interaction between group and time on EHAD, EHAB, and EHAD/EHAB ratio (P < 0.025). The intervention group demonstrated a 35.7% increase in EHAD (P < 0.001); a 20.3% increase in EHAB (P = 0.003), and 12.3% increase in EHAD/EHAB ratio (P = 0.019). No significant within-group differences were found in the control group (P > 0.335). Compliance was 91.25%, and median muscle soreness ranged from 0 to 2. The CA implemented in-season with an 8-week progressive training program elicited a large significant increase in EHAD, EHAB, and EHAD/EHAB ratio.

Effects of two different injury prevention resistance exercise protocols on the hamstring torque-angle relationship: a randomized controlled trial

The effects of two different 6-week lower body injury prevention programmes on knee muscle torque-angle relationship were examined in soccer players. Thirty-two men were randomly assigned to three groups: hamstring-eccentric (ECC) (n = 11), unstable-squatting (UNS) (n = 11), and control (n = 10). Intervention groups performed three training sessions per week using only three ECC or UNS exercises, respectively. Maximal peak knee flexion torque was measured at 35°, 45°, 60°, 80°, 90°, and 100°, pre- and post-intervention. Peak torque increased at 35° (P = 0.034, Cohen's d = 0.67) and 45° (P = 0.004, Cohen's d = 0.96) in the ECC group, and at 60° (P = 0.024, Cohen's d = 1.16), 80° (P = 0.018, Cohen's d = 1.21), and 90° (P = 0.001, Cohen's d = 1.38) in the UNS group. As these specific modifications might respectively and differentially protect athletes against hamstring and knee-joint injuries, the integration of both types of exercises should be considered when designing injury prevention programmes for soccer players.

Primary functions of the quadratus femoris and obturator externus muscles indicated from lengths and moment arms measured in mobilized cadavers

BACKGROUND

The small muscles of the pelvis and hip are often implicated in painful conditions. Although the quadratus femoris and obturator externus are usually described as external rotators of the hip, little is known about how they change their lengths and moment arms during human movement. Therefore, more precise measurements defining the positions and directions for their maximal strength and stretch are needed to better describe their functions and guide the clinical approach to pain.

METHODS

Repeated measurements of the muscle lengths and range of motion were obtained using wires simulating dissected muscles on human cadaver hips. The lengths were measured at every 15° of flexion with and without maximal range of ab/adduction, rotation, and combinations of the two motions. Measurements were obtained from normal hips (n=3), and movement-lengthening relations were later differentiated into movement-moment arm relations.

FINDINGS

The quadratus femoris showed maximum lengthening by flexion, adduction or abduction, and internal rotation, with the largest moment arms observed for extension in the deduced force-length efficient range of 60-90° flexion. The obturator externus showed maximum lengthening by extension, abduction, and internal rotation, with the largest moment arms observed for flexion and adduction in the deduced force-length efficient range around the hip's neutral position.

INTERPRETATION

Our findings indicate that maximal strength of the quadratus femoris muscle will be delivered in a flexed position towards extension, while maximal strength of the obturator externus muscle will be delivered in an extended position towards flexion and adduction.

Effects of isometric training on the knee extensor moment-angle relationship and vastus lateralis muscle architecture

PURPOSE

To analyse the muscle adaptations induced by two protocols of isometric training performed at different muscle lengths.

METHODS

Twenty-eight subjects were divided into three groups: one (K90) performed isometric training of the knee extensors at long muscle lengths (90° of knee flexion) for 8 weeks, and the second group (K50) at short muscle lengths (50°). The subjects of the third group acted as controls. Isokinetic dynamometry was utilized to analyse the net moment-angle relationship and vastus lateralis muscle thickness at three different locations, and pennation angles and fascicle length at 50 % of thigh length were measured at rest with ultrasonography.

RESULTS

Only subjects from K90 group showed significant increases in isokinetic strength (23.5%, P < 0.001), while K50 group showed no increases in isokinetic strength: (10%, P > 0.05). There was a shift in the angle of peak torque of the K90 group to longer muscle lengths (+14.6%, P = 0.002) with greater increases in isokinetic strength, while the K50 angle shifted to shorter muscle lengths (-7.3%, P = 0.039). Both training groups showed significant increases in muscle thickness, (K90 9-14% vs. K50 5-9%) but only K90 significantly increased their pennation angles (11.7%, P = 0.038). Fascicle lengths remained unchanged.

CONCLUSIONS

Isometric training at specific knee angles led to significant shifts of peak torque in the direction of the training muscle lengths. The greater strength gains and the architectural changes with training at long muscle lengths probably come from a combination of different factors, such as the different mechanical stresses placed upon the muscle-tendon complex.

Effects of a low volume injury prevention program on the hamstring torque angle relationship

The effects of a 4-week lower body injury prevention program on knee muscle torque-angle relationship were examined in soccer players. Twenty men were randomly allocated to either a control (n = 10) or training group (n = 10). The training group underwent three training sessions per week, comprising 3 sets of 8 repetitions of one open-chain exercise (Nordic curl) and two closed-chain exercises-forward lunges on a Bosu balance trainer and eccentric single leg dead lifts. Maximal peak knee flexion torque was measured at 35°, 45°, 60°, 80°, 90°, and 100° pre- and post-intervention. Significant improvements were observed only at 80° (p = .001; d = .94) along with a nonsignificant trend at 35° (p = .081; d = .43). As these modifications might protect athletes against muscle and joint injuries, the use of both stable-open and unstable-closed kinetic chain exercises emphasizing eccentric hamstring and knee stabilization actions should be integrated into injury prevention programs in team sports athletes.

[Current treatment concepts for muscular injuries]

Muscular lesions represent the most common form of sports injury. The four large muscle groups hamstrings, adductors, gastrocnemius and knee extensor muscles are most often affected. Most injuries occur during excentric tension impact. Diagnostics begin with an exact medical history and detailed clinical investigations. Imaging with ultrasound and magnetic resonance imaging (MRI) are important to differentiate between structural lesions and functional disorders and to determine the extent of the injury. Most frequently treatment remains conservative and is oriented to the three phases of the healing process. In most cases (leisure sports) the rest, ice, compression and elevation (RICE) concept with subsequent pain-adapted load increase suffices for a return to sport activities. Infiltration therapy including platelet-rich plasma (PRP) is an additional therapy option but should not be used to accelerate the healing process. Surgical treatment only rarely becomes necessary for treatment of muscular injuries.

The effects of eccentric exercise-induced muscle damage on running kinematics at different speeds

This study investigated the effects of knee localised muscle damage on running kinematics at varying speeds. Nineteen young women (23.2 ± 2.8 years; 164 ± 8 cm; 53.6 ± 5.4 kg), performed a maximal eccentric muscle damage protocol (5 × 15) of the knee extensors and flexors of both legs at 60 rad · s(-1). Lower body kinematics was assessed during level running on a treadmill at three speeds pre- and 48 h after. Evaluated muscle damage indices included isometric torque, muscle soreness and serum creatine kinase activity. The results revealed that all indices changed significantly after exercise, indicating muscle injury. Step length decreased and stride frequency significantly increased 48 h post-exercise only at the fastest running speed (3 m · s(-1)). Support time and knee flexion at toe-off increased only at the preferred transition speed and 2.5 m · s(-1). Knee flexion at foot contact, pelvic tilt and obliquity significantly increased, whereas hip extension during stance-phase, knee flexion during swing-phase, as well as knee and ankle joints range of motion significantly decreased 48 h post-exercise at all speeds. In conclusion, the effects of eccentric exercise of both knee extensors and flexors on particular tempo-spatial parameters and knee kinematics of running are speed-dependent. However, several pelvic and lower joint kinematics present similar behaviour at the three running speeds examined. These findings provide new insights into how running kinematics at different speeds are adapted to compensate for the impaired function of the knee musculature following muscle damage.

A comparison of two Hill-type skeletal muscle models on the construction of medial gastrocnemius length-tension curves in humans in vivo

Human length-tension curves are traditionally constructed using a model that assumes passive tension does not change during contraction ( model A) even though the animal literature suggests that passive tension can decrease ( model B). The study's aims were threefold: 1) measure differences in human medial gastrocnemius length-tension curves using model A vs. model B, 2) test the reliability of ultrasound constructed length-tension curves, and 3) test the robustness of fascicle length-generated length-tension curves to variations between the angle and fascicle length relationship. An isokinetic dynamometer manipulated and measured ankle angle while ultrasound was used to measure medial gastrocnemius fascicle length. Supramaximal tibial nerve stimulation was used to evoke resting muscle twitches. Length-tension curves were constructed using model A {angle-torque [A-T(A)], length-torque [L-T(A)]} or model B {length-torque [L-T(B)]} in three conditions: baseline, heel-lift (where the muscle was shortened at each angle), and baseline repeated 2 h later (+2 h). Length-tension curves constructed from model B differed from those produced via model A, indicated by a significant increase in maximum torque (≈23%) when using L-T(B) vs. L-T(A). No parameter measured was different between baseline and +2 h for any method, indicating good reliability when using ultrasound. Length-tension curves were unaffected by the heel-lift condition when using L-T(A) or L-T(B) but were affected when using A-T(A). Since the muscle model used significantly alters human length-tension curves, and given animal data indicate model B to be more accurate when passive tension is present, we recommend that model B should be used when constructing medial gastrocnemius length-tension curves in humans in vivo.

Selective strength loss and decreased muscle activity in hamstring injury

STUDY DESIGN

Cross-sectional, controlled laboratory study.

OBJECTIVES

To determine whether thigh muscle isokinetic torque patterns and activity, measured by electromyography (EMG), of individuals with hamstring injury differ from control individuals.

BACKGROUND

Neuromuscular control during thigh muscle strength assessment following hamstring injuries has not been reported.

METHODS

Fifteen athletes with prior hamstring injury (hamstring-injured group [HG]) were compared to 15 uninjured athletes (control group [CG]). The injuries were incurred 6 weeks to 12 months prior to participation, and all injured athletes had returned to at least partial training. Participants performed 5 isokinetic concentric extensor, concentric flexor, and eccentric flexor torque tests at 60°/s in the seated position. Peak torque was determined for each contraction type, as well as average torque for each of 4 time-based movement quartiles. EMG root-mean-squares were calculated in these movement quartiles for the biceps femoris and medial hamstrings.

RESULTS

No significant differences were found for peak torque for all contractions, when comparing HG injured and uninjured sides to CG bilateral averages. The HG injured limb eccentric flexor torque was significantly lower in the fourth quartile (approximately 25° to 5° knee flexion, hamstring lengthened range) compared to the CG bilateral average (P = .025). Eccentric flexor biceps femoris and hamstrings EMG root-mean-squares of the HG injured and the uninjured sides were significantly lower in the second to fourth quartiles (towards the lengthened range), compared to the CG bilateral averages (P<.05).

CONCLUSION

Decreased strength and EMG activation in a lengthened hamstrings range for the athletes with prior hamstring injury suggested a change in neuromuscular control. Lengthened range assessment of isokinetic eccentric flexor torque may be useful for the assessment of athletes with a prior injury; however, results should be confirmed with prospective studies.

A return-to-sport algorithm for acute hamstring injuries

Acute hamstring injuries are the most prevalent muscle injuries reported in sport. Despite a thorough and concentrated effort to prevent and rehabilitate hamstring injuries, injury occurrence and re-injury rates have not improved over the past 28 years. This failure is most likely due to the following: 1) an over-reliance on treating the symptoms of injury, such as subjective measures of "pain", with drugs and interventions; 2) the risk factors investigated for hamstring injuries have not been related to the actual movements that cause hamstring injuries i.e. not functional; and, 3) a multi-factorial approach to assessment and treatment has not been utilized. The purpose of this clinical commentary is to introduce a model for progression through a return-to-sport rehabilitation following an acute hamstring injury. This model is developed from objective and quantifiable tests (i.e. clinical and functional tests) that are structured into a step-by-step algorithm. In addition, each step in the algorithm includes a treatment protocol. These protocols are meant to help the athlete to improve through each phase safely so that they can achieve the desired goals and progress through the algorithm and back to their chosen sport. We hope that this algorithm can serve as a foundation for future evidence based research and aid in the development of new objective and quantifiable testing methods.

Muscle architecture and optimum angle of the knee flexors and extensors: a comparison between cyclists and Australian Rules football players

The purpose of this study was to investigate differences in optimum angle of peak torque (knee extensors and flexors) and muscle architecture (vastus lateralis) between 9 cyclists and 9 Australian Rules football (ARF) players. The angles of peak torque of the ARF players were significantly (p < 0.05) greater during knee extension (70.8 +/- 3.5 vs. 66.6 +/- 5.9 degrees) and smaller during knee flexion (26.2 +/- 2.9 vs. 32.3 +/- 3.8 degrees) compared with the cyclists. The ARF players had significantly (p < 0.05) smaller pennation angles (19.3 +/- 2.0 vs. 24.9 +/- 2.5 degrees) and longer fascicle lengths (7.9 +/- 0.7 vs. 6.2 +/- 0.8 cm) in comparison with the cyclists. There were no significant differences between groups regarding muscle thickness or peak torque ratios between the quadriceps and hamstrings. Muscle architectural changes associated with resistance strength training need to be investigated so that the effects of training on architecture and functional performance can be determined.

Effects of eccentric exercise on optimum length of the knee flexors and extensors during the preseason in professional soccer players

OBJECTIVE

To assess the effects of eccentric exercise on optimum lengths of the knee flexors and extensors during the preseason in professional soccer.

DESIGN

Twenty-eight athletes from a professional Spanish soccer team (Division II) were randomly assigned to an eccentric exercise intervention group (EG) or a control group (CG). Over the four-week period two athletes from the control group suffered RF injuries and two athletes were contracted by other clubs. After these exclusions, both groups (EG, n=13; and CG, n=11) performed regular soccer training during the four-week preseason period.

RESULTS

After the four weeks, the optimum lengths of the knee flexors were significantly (P<0.05) increased by 2.3 degrees in the CG and by 4.0 degrees in the EG. The change in the EG was significantly (P<0.05) greater than that of the CG. The optimum lengths of the knee extensors were significantly increased only in the EG by 6.5 degrees . Peak torque levels and ratios of quadriceps to hamstring (Q/H ratios) were not significantly altered throughout the study for either group.

CONCLUSION

Eccentric exercise can increase the optimum lengths of both the knee extensors and knee extensors flexors during the preseason in professional soccer.