A cross-sectional analysis of sagittal knee laxity and isokinetic muscle strength in soccer players

In this cross-sectional study, sagittal knee laxity and isokinetic strength of knee extensor and flexor muscle groups were measured and differences related to leg dominance were evaluated. A total of 44 healthy male soccer players (who had trained regularly at least for the last five years) and 44 sedentary people as their control counterparts were involved in this study. All participants were tested using a KT-1000 knee arthrometer for knee laxity. Isokinetic concentric knee peak torque and hamstring/quadriceps (H/Q) ratio were also measured at 60, 180, 300 degrees/s through a Cybex 2 - 340 dynamometer. Posterior laxity in the non-dominant side of soccer players was significantly higher than in the dominant side (p < 0.005) while there were no significant anterior and total anteroposterior (total AP) laxity differences in both groups. Soccer players had significantly lower anterior and total AP laxity values than controls (p < 0.0001) while there was no significant difference between posterior laxity values in both sides. Dominant extremity demonstrated significantly higher knee flexor peak torque and H/Q ratio at 180 degrees /s in soccer players (p < 0.05). Similarly in sedentary controls, H/Q ratio at 60 degrees /s of the dominant side was significantly higher than that in the non-dominant side (p < 0.05). Soccer players had significantly higher extensor and flexor peak torque values and H/Q ratios than sedentary subjects for both extremities. In both groups, there were no significant correlations between knee laxity and isokinetic knee extensor and flexor strength and H/Q ratios except weak negative correlation between posterior knee laxity and isokinetic extensor peak torque at 60, 180 and 300 degrees /s (p < 0.005, r = - 0.43, p < 0.05, r = - 0.39, p < 0.05, r = - 0.32 respectively) in the non-dominant side of soccer players and at 300 degrees /s (p < 0.05, r = - 0.32) in the non-dominant side of controls. Soccer players demonstrated significantly less sagittal knee laxity and higher isokinetic strength of the knee flexors and extensors compared to sedentary controls. Isokinetic strength difference was found to be higher for the flexor muscle group. Further prospective studies are needed to explain whether the increased H/Q ratio decreases the risk of ligamentous injury.     

Isokinetic strength testing does not predict hamstring injury in Australian Rules footballers

OBJECTIVE: To determine the relation of hamstring and quadriceps muscle strength and imbalance to hamstring injury using a prospective observational cohort study METHOD: A total of 102 senior male Australian Rules footballers aged 22.2 (3.6) years were tested at the start of a football season. Maximum voluntary concentric and eccentric torque of the hamstring and quadriceps muscles of both legs was assessed using a Kin-Com isokinetic dynamometer at angular velocities of 60 and 180 degrees/second. Twelve (11.8%) players sustained clinically diagnosed hamstring strains which caused them to miss one or more matches over the ensuing season. RESULTS: There were no significant differences for any of the isokinetic variables comparing the injured and non-injured legs in players with unilateral hamstring strains (n=9). Neither the injured nor the non-injured leg of injured players differed from the mean of left and right legs in non-injured players for any isokinetic variable. The hamstring to opposite hamstring ratios also did not differ between injured and non-injured players. A hamstring to opposite hamstring ratio of less than 0.90 and a hamstring to quadriceps ratio of less than 0.60 were not associated with an increased risk of hamstring injury. A significantly greater percentage of players who sustained a hamstring strain reported a history of hamstring strain compared with non-injured players (p=0.02). However, this was not related to muscle weakness or imbalance. CONCLUSIONS: Isokinetic muscle strength testing was not able to directly discriminate Australian Rules football players at risk for a hamstring injury.


     

Cutoffs of isokinetic strength ratio and hamstring strain prediction in professional soccer players

Hamstring strain injuries frequently occur during professional soccer practice. Low hamstring strength represents an intrinsic modifiable risk factor but cutoffs of isokinetic knee strength ratios are controversial to predict hamstring strain in professional soccer players. We aimed to predict hamstring strain in accordance with cutoffs of isokinetic knee strength ratios. Bilateral, conventional, and functional isokinetic strength ratios were calculated in 194 professional soccer players at the beginning of 15 consecutive seasons. 36 soccer players presented a moderate hamstring strain and 158 were not injured. The different calculated isokinetic ratios were compared with the right and left limb of the uninjured population. Different usual cutoffs were tested: at 0.85 and 0.90 for the bilateral concentric and eccentric hamstring‐to‐hamstring ratio, at 0.60 and 0.47 for the conventional hamstring‐to‐quadriceps ratio and at 0.80 and 1 for the mixed hamstring‐to‐quadriceps ratio. The specific ratios for the studied population were also determined by the 10th percentile and then tested. Hamstring strain prediction was established in terms of odds ratios. No cutoff with bilateral, conventional, or functional isokinetic strength ratio was predictive of hamstring strain after univariate analysis. Specific cutoffs determined from the studied population were not more predictive. Very few injured soccer players presented values under the cutoffs at 0.47 for the conventional ratio and at 0.80 for the mixed ratio. Regardless of their values, cutoffs of isokinetic strength ratios were not predictive of hamstring injuries. The use of isokinetic cutoffs is not recommended to predict hamstring muscle strain in professional soccer players.     

Isokinetic investigation of knee extensors and knee flexors in young French soccer players

The knee extensor and knee flexor muscle groups in three groups of young soccer players were tested with a Cybex II isokinetic dynamometer and compared with adults. Muscle strength increased with age. The largest gain was observed in young players aged 16-17 years whose quadriceps was the most modified muscle group giving the lowest H/Q ratio. Analysis of the regression equations obtained for torque values at 30 degrees s-1 and 180 degrees s-1 revealed that there were two distinct groups: under 16 and over 16. After reaching 16 years of age, the increase in muscle strength is greater at low velocity than at high velocity.     

Concentric quadriceps and hamstrings isokinetic strength in volleyball and soccer players

AIM: Muscular strength is one of the most important components of sport, both for high performance and for injury prevention. One of the most used methods to assess strength muscle balance between dominant (D)/non-dominant (ND) and antagonist/agonist is isokinetic testing. The main purpose of the present study was to describe and to compare isokinetic strength profiles (peak torque, bilateral strength differences between D/ND leg (BD) and hamstrings/quadriceps (H/Q) ratio) in athletes of different sports and positional roles. METHODS: Twenty-eight elite volleyball players and 47 pro soccer players (goalkeepers, n = 5; full-backs, n = 7; defenders, n = 10; midfielders, n = 15; forwards, n = 10) were evaluated using an isokinetic dynamometer (Biodex-System 2). Maximal gravity corrected concentric peak torque of knee extensor and flexor muscles were measured at angular velocities of 360 degrees x s(-1) (6.28 rad x s(-1)) and 90 degrees x s(-1) (1.57 rad x s(-1)). RESULTS: No significant BD were found between soccer and volleyball players with exception of hamstrings at 90 degrees x s(-1) (soccer: 10.6 +/- 8.0% vs volleyball: 6.9 +/- 5.5%). The H/Q ratio was significantly lower in volleyball players at 90 degrees x s(-1) (D: soccer 57.4 +/- 6.7% vs volleyball 50.4 +/- 7.2%; ND: soccer: 56.1 +/- 8.2% vs volleyball: 50.5 +/- 6.4%). No significant differences were found for BD and H/Q ratio in soccer players of different positional roles. CONCLUSION: In general, soccer and volleyball players do not seem to be different concerning BD although a significant difference was observed in hamstrings at 90 degrees x s(-1). Moreover, our data suggest that specific demands of these sports and the different positional roles in soccer did not induce bilateral leg imbalances. However, sport demands seem to influence isokinetic concentric H/Q ratio.     

Comparison of the decrease in strength between hamstrings and quadriceps during isokinetic fatigue testing in semiprofessional soccer players

An imbalance in the agonist/antagonist ratio has been identified as a pathologic factor. Using an isokinetic dynamometer, several studies have investigated the loss of quadriceps strength due to fatigue, but few have explored this phenomenon in the hamstrings. This study assessed the decline in strength of the hamstring and quadriceps muscles with fatigue. The goal was to determine whether a divergence in the decline in strength occurs that would affect the hamstring to quadriceps ratio of endurance. Twenty-seven professional soccer players were selected for endurance testing to evaluate fatigue on an isokinetic dynamometer. The decline in hamstring strength was significantly greater than that of the quadriceps after 15 repetitions for the dominant leg and after 40 repetitions for the nondominant leg. This study also revealed a decline in the endurance ratio compared with the maximal strength ratio in the dominant leg after 30 repetitions. In fatigue states, the decline in hamstring strength diverges from that of the quadriceps in both legs. This difference in resistance to fatigue provokes an imbalance that may affect the stabilizing function of the thigh muscles. These results can be considered as indicators of an increased risk of injury during exhausting effort.     

Isokinetic strength and anaerobic power of elite, subelite and amateur French soccer players

Information about the influence of different practice levels on physical characteristics of a large number of soccer players is lacking. Therefore we assessed muscular strength and anaerobic power of elite, subelite and amateur soccer players to clarify what parameters distinguish the top players from the less successful. We tested 95 soccer players from the French first division (elite), second division (subelite), and amateurs and determined the isokinetic strength of the knee extensor and flexor muscles at angular velocities from -120 degrees x s(-1) to 300 degrees x s(-1). Vertical jump, 10 m sprint, 30 m sprint and maximum ball speed during shooting were also measured. The elite players had higher knee flexor torque than the amateurs at all angular velocities (p < 0.05), except at 300 degrees x s(-1). The hamstring/quadriceps ratios proposed with two different methods were significantly lower in the amateur group than in the elite group (p < 0.05), except at 300 degrees x s(-1). Maximum ball speed during shooting and speed over 30 m sprint were not different between elite, subelite, and amateur players while speed over a 10 m sprint was significantly slower in amateur players and faster in the elite group (p < 0.05). Although performance in soccer is not determined only by measurable variables, professional players differ from amateurs in terms of knee flexor muscle strength and short-distance sprinting speed. Based on these findings we conclude that hamstring strength is extremely important in soccer players for joint stabilization during various tasks, notably in eccentric action. Further, short-sprinting performance may mirror actual game situations at high level and could be an important determinant of match-winning actions.     

Risk factors for leg injuries in female soccer players: a prospective investigation during one out-door season

The following possible risk factors for leg injuries in female soccer players were studied: age, anatomical alignment, generalized joint laxity, thigh muscle torque, muscle flexibility, ligamentous laxity of the knee and ankle joints, recent injuries, and duration of soccer exposure. A total of 146 players from 13 teams in the second and third Swedish divisions underwent clinical examination, isokinetic measurements of quadriceps and hamstring torques, and testing of postural sway of the legs. All soccer-related leg injuries resulting in absence from at least one scheduled practice session or game were recorded during one outdoor season (April-October). In 50 players there were 61 traumatic injuries, and 17 players sustained 19 overuse injuries. The overall injury incidence rate (traumatic and overuse) was 5.49/1000 h of soccer. Variables significantly increasing the risk of traumatic leg injuries included generalized joint laxity, low postural sway of the legs, hyperextension of the knee joint, and a low hamstring-to-quadriceps ratio during concentric action. Multivariate logistic regression showed hyperextension of the knee joint, a low postural sway, reduced H/Q ratio during concentric action, and a higher exposure to soccer to significantly increase the risk of traumatic leg injury. All five players who suffered an anterior cruciate ligament injury during the study period had a lower hamstring-to-quadriceps ratio during concentric action on the injured side than on their noninjured side.     

Effects of hamstring‐emphasized neuromuscular training on strength and sprinting mechanics in football players

The objective of this study was to examine the effects of a neuromuscular training program combining eccentric hamstring muscle strength, plyometrics, and free/resisted sprinting exercises on knee extensor/flexor muscle strength, sprinting performance, and horizontal mechanical properties of sprint running in football (soccer) players. Sixty footballers were randomly assigned to an experimental group (EG) or a control group (CG). Twenty‐seven players completed the EG and 24 players the CG. Both groups performed regular football training while the EG performed also a neuromuscular training during a 7‐week period. The EG showed a small increases in concentric quadriceps strength (ES = 0.38/0.58), a moderate to large increase in concentric (ES = 0.70/0.74) and eccentric (ES = 0.66/0.87) hamstring strength, and a small improvement in 5‐m sprint performance (ES = 0.32). By contrast, the CG presented lower magnitude changes in quadriceps (ES = 0.04/0.29) and hamstring (ES = 0.27/0.34) concentric muscle strength and no changes in hamstring eccentric muscle strength (ES = ?0.02/0.11). Thus, in contrast to the CG (ES = ?0.27/0.14), the EG showed an almost certain increase in the hamstring/quadriceps strength functional ratio (ES = 0.32/0.75). Moreover, the CG showed small magnitude impairments in sprinting performance (ES = ?0.35/?0.11). Horizontal mechanical properties of sprint running remained typically unchanged in both groups. These results indicate that a neuromuscular training program can induce positive hamstring strength and maintain sprinting performance, which might help in preventing hamstring strains in football players.     

Effects of eccentric versus concentric training on thigh muscle strength and EMG

The purpose of this study was to compare pure eccentric and concentric strength training regarding possible specific effects of muscle action type on neuromuscular parameters, such as a decreased inhibition during maximal voluntary eccentric actions. Two groups of young healthy adult men performed 10 weeks of either eccentric or concentric unilateral isokinetic knee extensor training at 90 degrees.s(-1), 4 sets of 10 maximal efforts, 3 days a week. Knee extensor torque and surface EMG from the quadriceps and hamstring muscle groups were collected and quantified in a window between 30 and 70 degrees knee angle (range of motion 90-5 degrees ) during maximal voluntary eccentric and concentric knee extensor actions at 30, 90, and 270 degrees.s(-1). Changes in strength of the trained legs revealed more signs of specificity related to velocity and contraction type after eccentric than concentric training. No major training effects were present in eccentric to concentric ratios of agonist EMG or in relative antagonist (hamstring) activation. Thus, for the trained leg, the muscle action type and speed specific changes in maximal voluntary eccentric strength could not be related to any effects on neural mechanisms, such as a selective increase in muscle activation during eccentric actions. Interestingly, with both types of training there were specific cross-education effects, that is, action type and velocity specific increases in strength occurred in the contralateral, untrained, leg, accompanied by a specific increase in eccentric to concentric EMG ratio after eccentric training.     

Force and power of preferred and non-preferred leg in young soccer players.

The purpose of this study was to assess the effects of soccer training on strength and power of leg extensor muscles in preadolescent boys and their possible influence in developing a muscular lateral dominance. Twenty male children (mean age 9.6 yr), ten soccer players and ten untrained subjects, participated in this study. Force and power were measured at five constant cranking velocities on an isokinetic bicycle dinamometer. Each isokinetic load was given after each trial. Force and power outputs were calculated for each limb. Soccer players always showed higher and statistically significant differences (p < 0.05) for force and power values for all considered pedal frequencies. No significant differences were observed for force and power values between preferred and non preferred limb. The results demonstrate the effect of soccer training on the increase of force and power of both legs regardless of lateral dominance.     

Knee isokinetic muscle strength and balance ratio in female soccer players of different age groups: a cross-sectional study

ABSTRACT

Background: As a consequence of years of soccer training and sexual maturation, there is an increase in lower body muscle mass and strength especially in the knee extensors and flexors muscles. In this context, the lack of knee joint stability, resulting from strength imbalance between knee extensor and flexors muscles, has been associated with knee injuries. The aim of this study was to compare the knee flexor and extensor muscle peak torque, average power, contralateral deficit, conventional and functional balance ratios of female soccer players from different age groups.

Methods: Sixty-six female soccer players were divided into four groups: under 13 (U13), under 15 (U15), under 17 (U17) years old and professional (PRO). Flexor and extensor knee muscle strength in concentric and eccentric actions of both limbs were assessed using isokinetic dynamometer.

Results: For the dominant limb, the knee concentric extensor muscles peak torques, assessed at 60 and at 240 deg/sec, and the average power of U15 group were significantly higher than U13 group. Extensor muscle average power of the PRO group was higher than U17. Dominant knee flexor average power of U15 was significantly higher than the U13 group. Peak torque at 60 deg/sec and 240 deg/sec and average power of the PRO group were higher than the U17 group. No differences were found regarding the eccentric action for flexor and extensor muscles. Conventional and functional balance ratios were similar among all age group, except for U13, which presented higher values than the U15 group for the dominant limb.

Conclusions: The greatest improvement in muscular performance occur when the athlete starts practicing soccer (after U13) and when they become professional (after U17) and the balance ratios, and muscle balance ratios remain stable in all age groups, although they are below the recommended level in the literature, which may increase the risk for lower limb injury.     

Acute effects of static stretching on peak torque and the hamstrings‐to‐quadriceps conventional and functional ratios

Recent evidence has shown acute static stretching may decrease hamstring‐to‐quadriceps (H:Q) ratios. However, the effects of static stretching on the functional H:Q ratio, which uses eccentric hamstrings muscle actions, have not been investigated. This study examined the acute effects of hamstrings and quadriceps static stretching on leg extensor and flexor concentric peak torque (PT), leg flexor eccentric PT, and the conventional and functional H:Q ratios. Twenty‐two women (mean ± SD age=20.6 ± 1.9 years; body mass=64.6 ± 9.1 kg; height=164.5 ± 6.4 cm) performed three maximal voluntary unilateral isokinetic leg extension, flexion, and eccentric hamstring muscle actions at the angular velocities of 60 and 180°/s before and after a bout of hamstrings, quadriceps, and combined hamstrings and quadriceps static stretching, and a control condition. Two‐way repeated measures ANOVAs (time × condition) were used to analyze the leg extension, flexion, and eccentric PT as well as the conventional and functional H:Q ratios. Results indicated that when collapsed across velocity, hamstrings‐only stretching decreased the conventional ratios (P<0.05). Quadriceps‐only and hamstrings and quadriceps stretching decreased the functional ratios (P<0.05). These findings suggested that stretching may adversely affect the conventional and functional H:Q ratios.     

Muscular strength, functional performances and injury risk in professional and junior elite soccer players

Muscle strength and anaerobic power of the lower extremities are neuromuscular variables that influence performance in many sports activities, including soccer. Despite frequent contradictions in the literature, it may be assumed that muscle strength and balance play a key role in targeted acute muscle injuries. The purpose of the present study was to provide and compare pre-season muscular strength and power profiles in professional and junior elite soccer players throughout the developmental years of 15-21. One original aspect of our study was that isokinetic data were considered alongside the past history of injury in these players. Fifty-seven elite and junior elite male soccer players were assigned to three groups: PRO, n=19; U-21, n=20 and U-17, n=18. Players benefited from knee flexor and extensor isokinetic testing consisting of concentric and eccentric exercises. A context of lingering muscle disorder was defined using statistically selected cut-offs. Functional performance was evaluated throughout a squat jump and 10 m sprint. The PRO group ran faster and jumped higher than the U-17 group (P<0.05). No significant difference in isokinetic muscle strength performance was observed between the three groups when considering normalized body mass parameters. Individual isokinetic profiles enabled the identification of 32/57 (56%) subjects presenting lower limb muscular imbalance. Thirty-six out of 57 players were identified as having sustained a previous major lower limb injury. Of these 36 players, 23 still showed significant muscular imbalance (64%). New trends in rational training could focus more on the risk of imbalance and implement antagonist strengthening aimed at injury prevention. Such an intervention would benefit not only athletes recovering from injury, but also uninjured players. An interdisciplinary approach involving trainers, a physical coach, and medical staff would be of interest to consider in implementing a prevention programme.     

Hamstring and ACL injuries impacts on hamstring-to-quadriceps ratio of the elite soccer players: A retrospective study

This study aimed to compare the angle-specific (AS) and non-angle-specific (NAS) hamstring to quadriceps conventional and functional ratios between healthy, hamstring- and ACL-injured elite soccer players. One hundred and eleven players (27.42 ± 8.01 years, 182.11 ± 6.79 cm, 75.93 ± 7.25 kg) completed a series of concentric knee flexor and extensor strength in addition to eccentric knee flexor strength was measured at an angular velocity of 60°.s⁻¹. Normalized and raw peak torque values, and the torque-angle profiles were extracted for analysis. Conventional and functional NAS (peak values) and AS (waveform ratios) hamstring to quadriceps ratios were calculated and compared between the groups. Healthy players produced greater functional and conventional ratios compared to players with either ACL or hamstring injury. Players with hamstring injury produced a lower AS functional ratios between 46° and 54° of knee flexion. Players suffering from ACL injury depicted a lower value for the AS functional ratio between 33° and 56° of knee flexion. Although NAS can identify soccer players with previous hamstring or ACL injury, the range where there is a strength deficiency is eluded. With the use of AS the range where the deficiency is present can be identified, and clinicians can benefit from this analysis to design robust rehabilitation protocols.     

Isokinetic torque levels for knee extensors and knee flexors in soccer players

The knee extensor and knee flexor strengths were measured isokinetically (30 degrees, 180 degrees/s) and isometrically with a Cybex II device in three groups of male soccer players (national team players, n = 13; division I, n = 15; division IV, n = 180) and a group of nonsoccer players (n = 32). There were difference in strength between soccer players and nonsoccer players and between players from different divisions. Correction for body surface area did not affect the results. The knee flexor/knee extensor ratio (H/Q ratio) was significantly higher for soccer players than for nonsoccer players. The fast-speed/slow-speed ratio for knee extensors was higher for nonsoccer players and for national team players than for players from divisions I and IV.     

Isokinetic knee extensor strength and functional performance in healthy female soccer players

östenberg A, Roos E, Ekdahl C, Roos H. Isokinetic knee extensor strength and functional performance in healthy female soccer players. The aims of this study were to determine the relationship between isokinetic knee extensor muscle strength at 60°/s and 180°/s and five functional performance tests (one-leg-hop, triple-jump, vertical-jump, one-leg-rising and square-hop), to determine the relationship between the five different functional performance tests and to present normative data and limb symmetry index concerning healthy female soccer players. In total 101 female soccer players ([Text Missing]X=20.3 years) were tested. A limb symmetry index, using weak/strong leg, varied from 83.9 to 96.3 in the tests. Between the functional performance tests there were in general correlations of r=0.4-0.8 (P<0.001). A correlation of r=0.77 (P<0.001) was obtained between one-leg-hop and triple-jump. No differences were found between the right and the left leg or the dominant and the non-dominant leg. Using linear regression models corrected for body weight, height and age, there were low correlations between the isokinetic strength measurements and the functional tests. It is not recommended using functional performance testing and isokinetic testing interchangeably.     

中国优秀U17男子足球运动员下肢肌肉力量比率与变向能力的关系

目的:探究中国优秀U17男子足球运动员的下肢腘绳肌/股四头肌肌力比率(hamstring/quadriceps ratio,H/Q比率)和变向能力的相关关系,为提升U17男子足球运动员的变向能力及预防下肢损伤提供依据。方法:对47名中国优秀U17男子足球运动员进行股四头肌和腘绳肌的向心收缩、离心收缩等速测试,并分别计算双下肢不同角速度下的传统H/Q比率(腘绳肌向心收缩峰值力矩/股四头肌向心收缩峰值力矩)和功能H/Q比率(腘绳肌离心收缩峰值力矩/股四头肌向心收缩峰值力矩)。同时,采用T型测试评价变向能力。采用皮尔逊相关探讨各比率和变向能力之间的相关性,并对存在相关的H/Q比率与变向能力进行多元回归分析。结果:非优势侧高速传统H/Q比率(r=0.44,P=0.002)、优势侧低速功能H/Q比率(r=-0.358,P=0.013)与T型测试成绩均存在显著性相关;两个变量可以共同解释T型测试成绩总方差的28.2%(R²=0.282,F=8.640,P<0.01)。结论:对于中国优秀U17男子足球运动员而言,优势侧低速功能H/Q比率越大、非优势侧高速传统H/Q比率越小...     

Effects of age on the reciprocal peak torque ratios during knee muscle contractions in elite soccer players

To investigate the effects of age on the reciprocal peak torque ratios during knee muscle contractions, 25 elite male soccer players, aged 22.3 +/- 3.8 yr (18-28), volunteered for the present study. The players were grouped as adult (> 21 years, n = 13) and young players (< or = 21 years, n = 12). Maximal concentric (CON) and eccentric (ECC) isokinetic thigh muscle strength was measured at angular velocities of 30 degrees, 180 degrees, 240 degrees and 300 degrees/s. ECC and CON peak torques of knee flexors (hamstring, HAM) and CON peak torques of knee extensors (quadriceps, QUA) in the dominant knee were greater (P < 0.05) in adult players than in young players at 180, 240 and 300 degrees/s. ECC HAM/CON QUA peak torque ratio at 300 degrees/s was greater (P < 0.05) for adult players compared to young players in the dominant knee but not in the nondominant knee. Furthermore, conventional HAM/QUA peak torque ratios of the dominant knee at all angular velocities for ECC contraction were higher (P < 0.05) in adult players than in young players. In conclusion, the findings of the present study indicate that the reciprocal torque ratio is influenced by age in the dominant knee of elite soccer players. Because there was no effect of age for the nondominant leg, the findings of the present study are more likely to be the result of the training background of the players than their age.     

Hamstring‐to‐quadriceps fatigue ratio offers new and different muscle function information than the conventional non‐fatigued ratio

Commonly used injury risk prediction tests such as the hamstring‐to‐quadriceps (H:Q) strength ratio appear to be poor predictors of non‐contact injury. However, these tests are typically performed in a non‐fatigued state, despite accumulated fatigue being an important risk factor for both hamstring strain (HS ) and anterior cruciate ligament (ACL ) injuries in professional soccer players. After the effect of different H:Q calculation methods were compared and contrasted, the influence of neuromuscular fatigue on the H:Q strength ratio and the association between fatigued and non‐fatigued ratio scores were examined. Thirty‐five professional soccer players performed a 30‐repetition isokinetic fatigue test protocol. Peak knee joint moments were computed for each repetition, and the H:Q conventional ratio (H:Q_CR ) was calculated using several different, previously published, methods. Knee extensor and flexor moments were statistically decreased by the sixth repetition and continued to decrease until the end of the protocol. However, the H:Q ratio was statistically decreased at the end of the test due to a significant reduction in knee flexor moment (correlation between change in knee flexor moment and change in H:Q, r ≈.80; P <.01). Moreover, H:Q measured in fatigue (ie, H:Q_{F atigue}) at the end of the test was greater than H:Q_CR (1.25‐1.38 vs 0.70, P <.01), these variables were weakly correlated (r =.39, P =.02), and subject rankings within the cohort based on H:Q_CR and H:Q_{F atigue} were different (r _s=0.25, P =.15). The present data suggest that H:Q ratio measurement during a fatiguing test (H:Q_{F atigue}) provides different outcomes to the traditional H:Q_CR . The observed significant hamstring fatigue and the difference, and weak correlation, between H:Q_CR and H:Q_{F atigue} indicate that useful information might be obtained with respect to the prediction of HS and ACL injury risk. The potential predictive value of H:Q_{F atigue} warrants validation in future prospective trials.