To investigate the role of eccentric knee flexor strength, between-limb imbalance and biceps femo... more To investigate the role of eccentric knee flexor strength, between-limb imbalance and biceps femoris long head (BFlh) fascicle length on the risk of future hamstring strain injury (HSI). Elite soccer players (n=152) from eight different teams participated. Eccentric knee flexor strength during the Nordic hamstring exercise and BFlh fascicle length were assessed at the beginning of preseason. The occurrences of HSIs following this were recorded by the team medical staff. Relative risk (RR) was determined for univariate data, and logistic regression was employed for multivariate data. Twenty seven new HSIs were reported. Eccentric knee flexor strength below 337 N (RR=4.4; 95% CI 1.1 to 17.5) and possessing BFlh fascicles shorter than 10.56 cm (RR=4.1; 95% CI 1.9 to 8.7) significantly increased the risk of a HSI. Multivariate logistic regression revealed significant effects when combinations of age, history of HSI, eccentric knee flexor strength and BFlh fascicle length were explored. From these analyses the likelihood of a future HSI in older athletes or those with a HSI history was reduced if high levels of eccentric knee flexor strength and longer BFlh fascicles were present. The presence of short BFlh fascicles and low levels of eccentric knee flexor strength in elite soccer players increases the risk of future HSI. The greater risk of a future HSI in older players or those with a previous HSI is reduced when they have longer BFlh fascicles and high levels of eccentric strength.
Hamstring strain injuries (HSIs) are the most common injury type in Australian football, and the ... more Hamstring strain injuries (HSIs) are the most common injury type in Australian football, and the rate of recurrence has been consistently high for a number of years. Long-lasting neuromuscular inhibition has been noted in previously injured athletes, but it is not known if this influences the athlete's adaptive response to training. To determine if elite Australian footballers with a prior unilateral HSI (previously injured group) display less improvement in eccentric hamstring strength during preseason training compared with athletes without a history of HSIs (control group). Cohort study; Level of evidence, 2. A total of 99 elite Australian footballers (17 with a history of unilateral HSIs in the previous 12-month period) participated in this study. Eccentric hamstring strength was assessed at the start and end of preseason training using an instrumented Nordic hamstring device. The change in eccentric strength across the preseason was determined in absolute terms and normaliz...
To systematically review the evidence base related to hamstring strength and flexibility in previ... more To systematically review the evidence base related to hamstring strength and flexibility in previously injured hamstrings. Systematic review and meta-analysis. A systematic literature search was conducted of PubMed, CINAHL, SPORTDiscus, Cochrane Library, Web of Science and EMBASE from inception to August 2015. Full-text English articles which included studies which assessed at least one measure of hamstring strength or flexibility in men and women with prior hamstring strain injury within 24 months of the testing date. Twenty-eight studies were included in the review. Previously injured legs demonstrated deficits across several variables. Lower isometric strength was found <7 days postinjury (d=-1.72), but this did not persist beyond 7 days after injury. The passive straight leg raise was restricted at multiple time points after injury (<10 days, d=-1.12; 10-20 days, d=-0.74; 20-30 days, d=-0.40), but not after 40-50 days postinjury. Deficits remained after return to play in i...
Faculty of Health Institute of Health and Biomedical Innovation School of Exercise Nutrition Sciences, 2012
Hamstring strain injuries (HSI) are the predominant non-contact injury in many sports. Intermitte... more Hamstring strain injuries (HSI) are the predominant non-contact injury in many sports. Intermittent running has been shown to result in preferential reductions in eccentric hamstring strength, which may increase the risk of sustaining a HSI. The eccentric specific nature of this decline in hamstring function implicates central mechanisms, as peripheral fatigue mechanisms tend to impact upon both concentric and eccentric contractions modes. However, the median power frequency (MPF) of the surface electromyography signal has yet to be examined in the fatigued hamstring following intermittent sprint running.
PURPOSE: To determine the impact of fatigue induced by intermittent sprinting on the MPF of the medial and lateral hamstring muscles.
METHODS: Fifteen recreationally active males completed 18 × 20m overground sprints. Maximal strength (concentric and eccentric knee flexor and concentric knee extensor) was determined isokinetically at the velocities of ±1800.s-1 and ±600.s-1 while hamstring muscle activation was assessed using surface electromyography, before and 15 minutes after the running protocol.
RESULTS: Overground intermittent sprint running caused a significant reduction in eccentric knee flexor strength (27.2 Nm; 95% CI = 11.2 to 43.3; p=0.0001) but not concentric strength (9.3 Nm; 95% CI = -6.7 to 25.3; P=0.6361). Following intermittent sprinting, MPF of the lateral hamstrings showed a significant decline eccentrically at both -1800.s-1 (5.26; 95% CI = 0.34 to 9.84; p=0.0452) and -600.s-1(2.96; 95% CI = 0.15 to 7.54; p=0.0347). However, there was no significant decline concentrically at either speeds (p>0.05). Furthermore, there were also no significant declines in the medial hamstring MPF following intermittent sprinting (p>0.05).
CONCLUSION: Sprint running induced fatigue led to an eccentric specific reduction in knee flexor torque, as well as a decline in eccentric, lateral hamstring MPF. Furthermore, MPF was suppressed across both contraction modes for the medial hamstrings. These findings indicate that fatigue is associated with the declines in MPF of the lateral hamstrings following intermittent sprint running. However, this decline is potentially contraction mode specific, with decreases in MPF only occurring during eccentric contractions. This association between fatigue and MPF may also indicate that conduction rates and fibre type recruitment of the lateral hamstrings, during eccentric contractions may be significantly altered following sprint running.
The architectural characteristics of muscle (fascicle length, pennation angle muscle thickness) r... more The architectural characteristics of muscle (fascicle length, pennation angle muscle thickness) respond to varying forms of stimuli (eg, training, immobilisation and injury). Architectural changes following injury are thought to occur in response to the restricted range of motion experienced during rehabilitation and the associated neuromuscular inhibition. However, it is unknown if these differences exist prior to injury, and had a role in injury occuring (prospectively), or if they occur in response to the incident itself (retrospectively). Considering that the structure of a muscle will influence how it functions, it is of interest to understand how these architectural variations may alter how a muscle acts with reference to the force-length and force-velocity relationships. Our narrative review provides an overview of muscle architectural adaptations to training and injury. Specifically, we (1) describe the methods used to measure muscle architecture; (2) detail the impact that ...
To investigate the role of eccentric knee flexor strength, between-limb imbalance and biceps femo... more To investigate the role of eccentric knee flexor strength, between-limb imbalance and biceps femoris long head (BFlh) fascicle length on the risk of future hamstring strain injury (HSI). Elite soccer players (n=152) from eight different teams participated. Eccentric knee flexor strength during the Nordic hamstring exercise and BFlh fascicle length were assessed at the beginning of preseason. The occurrences of HSIs following this were recorded by the team medical staff. Relative risk (RR) was determined for univariate data, and logistic regression was employed for multivariate data. Twenty seven new HSIs were reported. Eccentric knee flexor strength below 337 N (RR=4.4; 95% CI 1.1 to 17.5) and possessing BFlh fascicles shorter than 10.56 cm (RR=4.1; 95% CI 1.9 to 8.7) significantly increased the risk of a HSI. Multivariate logistic regression revealed significant effects when combinations of age, history of HSI, eccentric knee flexor strength and BFlh fascicle length were explored. From these analyses the likelihood of a future HSI in older athletes or those with a HSI history was reduced if high levels of eccentric knee flexor strength and longer BFlh fascicles were present. The presence of short BFlh fascicles and low levels of eccentric knee flexor strength in elite soccer players increases the risk of future HSI. The greater risk of a future HSI in older players or those with a previous HSI is reduced when they have longer BFlh fascicles and high levels of eccentric strength.
Hamstring strain injuries are the predominant injury in many sports, costing athletes and clubs a... more Hamstring strain injuries are the predominant injury in many sports, costing athletes and clubs a significant financial and performance burden; therefore, the ability to identify and intervene with individuals who are considered at high risk of injury is important. One measure that has grown in popularity as an outcome variable following hamstring intervention/prevention studies and rehabilitation is the angle of peak knee flexor torque. This current opinion article will firstly introduce the measure and the processes behind it. Second, the article will summarise how the angle of peak knee flexor torque has been suggested to measure hamstring strain injury risk. Finally, the numerous limitations will be presented and the article will outline how these limitations may influence the usefulness of the angle of peak knee flexor torque measure. These include the lack of muscle specificity, the common concentric contraction mode of assessment, reliability of the measure, various neural co...
To determine if limbs with a history of anterior cruciate ligament (ACL) injury reconstructed fro... more To determine if limbs with a history of anterior cruciate ligament (ACL) injury reconstructed from the semitendinosus (ST) display different biceps femoris long head (BFlh) architecture and eccentric strength, assessed during the Nordic hamstring exercise, compared to the contralateral uninjured limb. The architectural characteristics of the BFlh were assessed at rest and at 25% of a maximal voluntary isometric contraction (MVIC) in the control (n=52) and previous ACL injury group (n=15) using two-dimensional ultrasonography. Eccentric knee-flexor strength was assessed during the Nordic hamstring exercise. Fascicle length was shorter (p=0.001; d range: 0.90 to 1.31) and pennation angle (p range: 0.001 to 0.006: d range: 0.87 to 0.93) was greater in the BFlh of the ACL injured limb when compared to the contralateral uninjured limb at rest and during 25% of MVIC. Eccentric strength was significantly lower in the ACL injured limb than the contralateral uninjured limb (-13.7%; -42.9N; 9...
Medicine and science in sports and exercise, Jan 12, 2015
To determine i) the architectural adaptations of the biceps femoris long head (BFlf) following co... more To determine i) the architectural adaptations of the biceps femoris long head (BFlf) following concentric or eccentric strength training interventions; ii) the time course of adaptation during training and detraining. Participants in this randomized controlled trial (control [n=28], concentric training group [n=14], eccentric training group [n=14], males) completed a 4-week control period, followed by 6 weeks of either concentric- or eccentric-only knee flexor training on an isokinetic dynamometer and finished with 28 days of detraining. Architectural characteristics of BFlf were assessed at rest and during graded isometric contractions utilizing two-dimensional ultrasonography at 28 days pre-baseline, baseline, days 14, 21 and 42 of the intervention and then again following 28 days of detraining. BFlf fascicle length was significantly longer in the eccentric training group (p<0.05, d range: 2.65 to 2.98) and shorter in the concentric training group (p<0.05, d range: -1.62 to ...
Hamstring strain injuries (HSIs) are the most common injury type in Australian football, and the ... more Hamstring strain injuries (HSIs) are the most common injury type in Australian football, and the rate of recurrence has been consistently high for a number of years. Long-lasting neuromuscular inhibition has been noted in previously injured athletes, but it is not known if this influences the athlete's adaptive response to training. To determine if elite Australian footballers with a prior unilateral HSI (previously injured group) display less improvement in eccentric hamstring strength during preseason training compared with athletes without a history of HSIs (control group). Cohort study; Level of evidence, 2. A total of 99 elite Australian footballers (17 with a history of unilateral HSIs in the previous 12-month period) participated in this study. Eccentric hamstring strength was assessed at the start and end of preseason training using an instrumented Nordic hamstring device. The change in eccentric strength across the preseason was determined in absolute terms and normaliz...
PURPOSE: Are eccentric hamstring strength and between-limb imbalance in eccentric strength, measu... more PURPOSE: Are eccentric hamstring strength and between-limb imbalance in eccentric strength, measured during the Nordic hamstring exercise, risk factors for hamstring strain injury (HSI)?METHODS: Elite Australian footballers (n = 210) from five different teams participated. Eccentric hamstring strength during the Nordic exercise was obtained at the commencement and conclusion of preseason training and at the midpoint of the season. Injury history and demographic data were also collected. Reports on prospectively occurring HSI were completed by the team medical staff. Relative risk (RR) was determined for univariate data, and logistic regression was employed for multivariate data.RESULTS: Twenty-eight new HSI were recorded. Eccentric hamstring strength below 256 N at the start of the preseason and 279 N at the end of the preseason increased the risk of future HSI 2.7-fold (RR, 2.7; 95% confidence interval, 1.3 to 5.5; P = 0.006) and 4.3-fold (RR, 4.3; 95% confidence interval, 1.7 to 11.0; P = 0.002), respectively. Between-limb imbalance in strength of greater than 10% did not increase the risk of future HSI. Univariate analysis did not reveal a significantly greater RR for future HSI in athletes who had sustained a lower limb injury of any kind within the last 12 months. Logistic regression revealed interactions between both athlete age and history of HSI with eccentric hamstring strength, whereby the likelihood of future HSI in older athletes or athletes with a history of HSI was reduced if an athlete had high levels of eccentric strength.CONCLUSION: Low levels of eccentric hamstring strength increased the risk of future HSI. Interaction effects suggest that the additional risk of future HSI associated with advancing age or previous injury was mitigated by higher levels of eccentric hamstring strength.
Scandinavian Journal of Medicine & Science in Sports, 2014
The aim of this study was to determine whether declines in knee flexor strength following overgro... more The aim of this study was to determine whether declines in knee flexor strength following overground repeat sprints were related to changes in hamstrings myoelectrical activity. Seventeen recreationally active men completed maximal isokinetic concentric and eccentric knee flexor strength assessments at 180°/s before and after repeat sprint running. Myoelectrical activity of the biceps femoris (BF) and medial hamstrings (MHs) was measured during all isokinetic contractions. Repeated measures mixed model [fixed factors = time (pre- and post-repeat sprint) and leg (dominant and nondominant), random factor = participants] design was fitted with the restricted maximal likelihood method. Repeat sprint running resulted in significant declines in eccentric, and concentric, knee flexor strength (eccentric = 26 ± 4 Nm, 15% P &lt; 0.001; concentric 11 ± 2 Nm, 10% P &lt; 0.001). Eccentric BF myoelectrical activity was significantly reduced (10%; P = 0.035). Concentric BF and all MH myoelectrical activity were not altered. The declines in maximal eccentric torque were associated with the change in eccentric BF myoelectrical activity (P = 0.013). Following repeat sprint running, there were preferential declines in the myoelectrical activity of the BF, which explained declines in eccentric knee flexor strength.
The aim of this study was to determine if athletes with a history of hamstring strain injury disp... more The aim of this study was to determine if athletes with a history of hamstring strain injury display lower levels of surface EMG (sEMG) activity and median power frequency in the previously injured hamstring muscle during maximal voluntary contractions. Recreational athletes were recruited, 13 with a history of unilateral hamstring strain injury and 15 without prior injury. All athletes undertook isokinetic dynamometry testing of the knee flexors and sEMG assessment of the biceps femoris long head (BF) and medial hamstrings (MHs) during concentric and eccentric contractions at ±180 and ±60°s(-1). The knee flexors on the previously injured limb were weaker at all contraction speeds compared to the uninjured limb (+180°s(-1)p=0.0036; +60°s(-1)p=0.0013; -60°s(-1)p=0.0007; -180°s(-1)p=0.0007) whilst sEMG activity was only lower in the BF during eccentric contractions (-60°s(-1)p=0.0025; -180°s(-1)p=0.0003). There were no between limb differences in MH sEMG activity or median power frequency from either BF or MH in the injured group. The uninjured group showed no between limb differences in any of the tested variables. Secondary analysis comparing the between limb difference in the injured and the uninjured groups, confirmed that previously injured hamstrings were mostly weaker (+180°s(-1)p=0.2208; +60°s(-1)p=0.0379; -60°(-1)p=0.0312; -180°s(-1)p=0.0110) and that deficits in sEMG were confined to the BF during eccentric contractions (-60°s(-1)p=0.0542; -180°s(-1)p=0.0473). Previously injured hamstrings were weaker and BF sEMG activity was lower than the contralateral uninjured hamstring. This has implications for hamstring strain injury prevention and rehabilitation which should consider altered neural function following hamstring strain injury.
To investigate the role of eccentric knee flexor strength, between-limb imbalance and biceps femo... more To investigate the role of eccentric knee flexor strength, between-limb imbalance and biceps femoris long head (BFlh) fascicle length on the risk of future hamstring strain injury (HSI). Elite soccer players (n=152) from eight different teams participated. Eccentric knee flexor strength during the Nordic hamstring exercise and BFlh fascicle length were assessed at the beginning of preseason. The occurrences of HSIs following this were recorded by the team medical staff. Relative risk (RR) was determined for univariate data, and logistic regression was employed for multivariate data. Twenty seven new HSIs were reported. Eccentric knee flexor strength below 337 N (RR=4.4; 95% CI 1.1 to 17.5) and possessing BFlh fascicles shorter than 10.56 cm (RR=4.1; 95% CI 1.9 to 8.7) significantly increased the risk of a HSI. Multivariate logistic regression revealed significant effects when combinations of age, history of HSI, eccentric knee flexor strength and BFlh fascicle length were explored. From these analyses the likelihood of a future HSI in older athletes or those with a HSI history was reduced if high levels of eccentric knee flexor strength and longer BFlh fascicles were present. The presence of short BFlh fascicles and low levels of eccentric knee flexor strength in elite soccer players increases the risk of future HSI. The greater risk of a future HSI in older players or those with a previous HSI is reduced when they have longer BFlh fascicles and high levels of eccentric strength.
Hamstring strain injuries (HSIs) are the most common injury type in Australian football, and the ... more Hamstring strain injuries (HSIs) are the most common injury type in Australian football, and the rate of recurrence has been consistently high for a number of years. Long-lasting neuromuscular inhibition has been noted in previously injured athletes, but it is not known if this influences the athlete's adaptive response to training. To determine if elite Australian footballers with a prior unilateral HSI (previously injured group) display less improvement in eccentric hamstring strength during preseason training compared with athletes without a history of HSIs (control group). Cohort study; Level of evidence, 2. A total of 99 elite Australian footballers (17 with a history of unilateral HSIs in the previous 12-month period) participated in this study. Eccentric hamstring strength was assessed at the start and end of preseason training using an instrumented Nordic hamstring device. The change in eccentric strength across the preseason was determined in absolute terms and normaliz...
To systematically review the evidence base related to hamstring strength and flexibility in previ... more To systematically review the evidence base related to hamstring strength and flexibility in previously injured hamstrings. Systematic review and meta-analysis. A systematic literature search was conducted of PubMed, CINAHL, SPORTDiscus, Cochrane Library, Web of Science and EMBASE from inception to August 2015. Full-text English articles which included studies which assessed at least one measure of hamstring strength or flexibility in men and women with prior hamstring strain injury within 24 months of the testing date. Twenty-eight studies were included in the review. Previously injured legs demonstrated deficits across several variables. Lower isometric strength was found <7 days postinjury (d=-1.72), but this did not persist beyond 7 days after injury. The passive straight leg raise was restricted at multiple time points after injury (<10 days, d=-1.12; 10-20 days, d=-0.74; 20-30 days, d=-0.40), but not after 40-50 days postinjury. Deficits remained after return to play in i...
Faculty of Health Institute of Health and Biomedical Innovation School of Exercise Nutrition Sciences, 2012
Hamstring strain injuries (HSI) are the predominant non-contact injury in many sports. Intermitte... more Hamstring strain injuries (HSI) are the predominant non-contact injury in many sports. Intermittent running has been shown to result in preferential reductions in eccentric hamstring strength, which may increase the risk of sustaining a HSI. The eccentric specific nature of this decline in hamstring function implicates central mechanisms, as peripheral fatigue mechanisms tend to impact upon both concentric and eccentric contractions modes. However, the median power frequency (MPF) of the surface electromyography signal has yet to be examined in the fatigued hamstring following intermittent sprint running.
PURPOSE: To determine the impact of fatigue induced by intermittent sprinting on the MPF of the medial and lateral hamstring muscles.
METHODS: Fifteen recreationally active males completed 18 × 20m overground sprints. Maximal strength (concentric and eccentric knee flexor and concentric knee extensor) was determined isokinetically at the velocities of ±1800.s-1 and ±600.s-1 while hamstring muscle activation was assessed using surface electromyography, before and 15 minutes after the running protocol.
RESULTS: Overground intermittent sprint running caused a significant reduction in eccentric knee flexor strength (27.2 Nm; 95% CI = 11.2 to 43.3; p=0.0001) but not concentric strength (9.3 Nm; 95% CI = -6.7 to 25.3; P=0.6361). Following intermittent sprinting, MPF of the lateral hamstrings showed a significant decline eccentrically at both -1800.s-1 (5.26; 95% CI = 0.34 to 9.84; p=0.0452) and -600.s-1(2.96; 95% CI = 0.15 to 7.54; p=0.0347). However, there was no significant decline concentrically at either speeds (p>0.05). Furthermore, there were also no significant declines in the medial hamstring MPF following intermittent sprinting (p>0.05).
CONCLUSION: Sprint running induced fatigue led to an eccentric specific reduction in knee flexor torque, as well as a decline in eccentric, lateral hamstring MPF. Furthermore, MPF was suppressed across both contraction modes for the medial hamstrings. These findings indicate that fatigue is associated with the declines in MPF of the lateral hamstrings following intermittent sprint running. However, this decline is potentially contraction mode specific, with decreases in MPF only occurring during eccentric contractions. This association between fatigue and MPF may also indicate that conduction rates and fibre type recruitment of the lateral hamstrings, during eccentric contractions may be significantly altered following sprint running.
The architectural characteristics of muscle (fascicle length, pennation angle muscle thickness) r... more The architectural characteristics of muscle (fascicle length, pennation angle muscle thickness) respond to varying forms of stimuli (eg, training, immobilisation and injury). Architectural changes following injury are thought to occur in response to the restricted range of motion experienced during rehabilitation and the associated neuromuscular inhibition. However, it is unknown if these differences exist prior to injury, and had a role in injury occuring (prospectively), or if they occur in response to the incident itself (retrospectively). Considering that the structure of a muscle will influence how it functions, it is of interest to understand how these architectural variations may alter how a muscle acts with reference to the force-length and force-velocity relationships. Our narrative review provides an overview of muscle architectural adaptations to training and injury. Specifically, we (1) describe the methods used to measure muscle architecture; (2) detail the impact that ...
To investigate the role of eccentric knee flexor strength, between-limb imbalance and biceps femo... more To investigate the role of eccentric knee flexor strength, between-limb imbalance and biceps femoris long head (BFlh) fascicle length on the risk of future hamstring strain injury (HSI). Elite soccer players (n=152) from eight different teams participated. Eccentric knee flexor strength during the Nordic hamstring exercise and BFlh fascicle length were assessed at the beginning of preseason. The occurrences of HSIs following this were recorded by the team medical staff. Relative risk (RR) was determined for univariate data, and logistic regression was employed for multivariate data. Twenty seven new HSIs were reported. Eccentric knee flexor strength below 337 N (RR=4.4; 95% CI 1.1 to 17.5) and possessing BFlh fascicles shorter than 10.56 cm (RR=4.1; 95% CI 1.9 to 8.7) significantly increased the risk of a HSI. Multivariate logistic regression revealed significant effects when combinations of age, history of HSI, eccentric knee flexor strength and BFlh fascicle length were explored. From these analyses the likelihood of a future HSI in older athletes or those with a HSI history was reduced if high levels of eccentric knee flexor strength and longer BFlh fascicles were present. The presence of short BFlh fascicles and low levels of eccentric knee flexor strength in elite soccer players increases the risk of future HSI. The greater risk of a future HSI in older players or those with a previous HSI is reduced when they have longer BFlh fascicles and high levels of eccentric strength.
Hamstring strain injuries are the predominant injury in many sports, costing athletes and clubs a... more Hamstring strain injuries are the predominant injury in many sports, costing athletes and clubs a significant financial and performance burden; therefore, the ability to identify and intervene with individuals who are considered at high risk of injury is important. One measure that has grown in popularity as an outcome variable following hamstring intervention/prevention studies and rehabilitation is the angle of peak knee flexor torque. This current opinion article will firstly introduce the measure and the processes behind it. Second, the article will summarise how the angle of peak knee flexor torque has been suggested to measure hamstring strain injury risk. Finally, the numerous limitations will be presented and the article will outline how these limitations may influence the usefulness of the angle of peak knee flexor torque measure. These include the lack of muscle specificity, the common concentric contraction mode of assessment, reliability of the measure, various neural co...
To determine if limbs with a history of anterior cruciate ligament (ACL) injury reconstructed fro... more To determine if limbs with a history of anterior cruciate ligament (ACL) injury reconstructed from the semitendinosus (ST) display different biceps femoris long head (BFlh) architecture and eccentric strength, assessed during the Nordic hamstring exercise, compared to the contralateral uninjured limb. The architectural characteristics of the BFlh were assessed at rest and at 25% of a maximal voluntary isometric contraction (MVIC) in the control (n=52) and previous ACL injury group (n=15) using two-dimensional ultrasonography. Eccentric knee-flexor strength was assessed during the Nordic hamstring exercise. Fascicle length was shorter (p=0.001; d range: 0.90 to 1.31) and pennation angle (p range: 0.001 to 0.006: d range: 0.87 to 0.93) was greater in the BFlh of the ACL injured limb when compared to the contralateral uninjured limb at rest and during 25% of MVIC. Eccentric strength was significantly lower in the ACL injured limb than the contralateral uninjured limb (-13.7%; -42.9N; 9...
Medicine and science in sports and exercise, Jan 12, 2015
To determine i) the architectural adaptations of the biceps femoris long head (BFlf) following co... more To determine i) the architectural adaptations of the biceps femoris long head (BFlf) following concentric or eccentric strength training interventions; ii) the time course of adaptation during training and detraining. Participants in this randomized controlled trial (control [n=28], concentric training group [n=14], eccentric training group [n=14], males) completed a 4-week control period, followed by 6 weeks of either concentric- or eccentric-only knee flexor training on an isokinetic dynamometer and finished with 28 days of detraining. Architectural characteristics of BFlf were assessed at rest and during graded isometric contractions utilizing two-dimensional ultrasonography at 28 days pre-baseline, baseline, days 14, 21 and 42 of the intervention and then again following 28 days of detraining. BFlf fascicle length was significantly longer in the eccentric training group (p<0.05, d range: 2.65 to 2.98) and shorter in the concentric training group (p<0.05, d range: -1.62 to ...
Hamstring strain injuries (HSIs) are the most common injury type in Australian football, and the ... more Hamstring strain injuries (HSIs) are the most common injury type in Australian football, and the rate of recurrence has been consistently high for a number of years. Long-lasting neuromuscular inhibition has been noted in previously injured athletes, but it is not known if this influences the athlete's adaptive response to training. To determine if elite Australian footballers with a prior unilateral HSI (previously injured group) display less improvement in eccentric hamstring strength during preseason training compared with athletes without a history of HSIs (control group). Cohort study; Level of evidence, 2. A total of 99 elite Australian footballers (17 with a history of unilateral HSIs in the previous 12-month period) participated in this study. Eccentric hamstring strength was assessed at the start and end of preseason training using an instrumented Nordic hamstring device. The change in eccentric strength across the preseason was determined in absolute terms and normaliz...
PURPOSE: Are eccentric hamstring strength and between-limb imbalance in eccentric strength, measu... more PURPOSE: Are eccentric hamstring strength and between-limb imbalance in eccentric strength, measured during the Nordic hamstring exercise, risk factors for hamstring strain injury (HSI)?METHODS: Elite Australian footballers (n = 210) from five different teams participated. Eccentric hamstring strength during the Nordic exercise was obtained at the commencement and conclusion of preseason training and at the midpoint of the season. Injury history and demographic data were also collected. Reports on prospectively occurring HSI were completed by the team medical staff. Relative risk (RR) was determined for univariate data, and logistic regression was employed for multivariate data.RESULTS: Twenty-eight new HSI were recorded. Eccentric hamstring strength below 256 N at the start of the preseason and 279 N at the end of the preseason increased the risk of future HSI 2.7-fold (RR, 2.7; 95% confidence interval, 1.3 to 5.5; P = 0.006) and 4.3-fold (RR, 4.3; 95% confidence interval, 1.7 to 11.0; P = 0.002), respectively. Between-limb imbalance in strength of greater than 10% did not increase the risk of future HSI. Univariate analysis did not reveal a significantly greater RR for future HSI in athletes who had sustained a lower limb injury of any kind within the last 12 months. Logistic regression revealed interactions between both athlete age and history of HSI with eccentric hamstring strength, whereby the likelihood of future HSI in older athletes or athletes with a history of HSI was reduced if an athlete had high levels of eccentric strength.CONCLUSION: Low levels of eccentric hamstring strength increased the risk of future HSI. Interaction effects suggest that the additional risk of future HSI associated with advancing age or previous injury was mitigated by higher levels of eccentric hamstring strength.
Scandinavian Journal of Medicine & Science in Sports, 2014
The aim of this study was to determine whether declines in knee flexor strength following overgro... more The aim of this study was to determine whether declines in knee flexor strength following overground repeat sprints were related to changes in hamstrings myoelectrical activity. Seventeen recreationally active men completed maximal isokinetic concentric and eccentric knee flexor strength assessments at 180°/s before and after repeat sprint running. Myoelectrical activity of the biceps femoris (BF) and medial hamstrings (MHs) was measured during all isokinetic contractions. Repeated measures mixed model [fixed factors = time (pre- and post-repeat sprint) and leg (dominant and nondominant), random factor = participants] design was fitted with the restricted maximal likelihood method. Repeat sprint running resulted in significant declines in eccentric, and concentric, knee flexor strength (eccentric = 26 ± 4 Nm, 15% P &lt; 0.001; concentric 11 ± 2 Nm, 10% P &lt; 0.001). Eccentric BF myoelectrical activity was significantly reduced (10%; P = 0.035). Concentric BF and all MH myoelectrical activity were not altered. The declines in maximal eccentric torque were associated with the change in eccentric BF myoelectrical activity (P = 0.013). Following repeat sprint running, there were preferential declines in the myoelectrical activity of the BF, which explained declines in eccentric knee flexor strength.
The aim of this study was to determine if athletes with a history of hamstring strain injury disp... more The aim of this study was to determine if athletes with a history of hamstring strain injury display lower levels of surface EMG (sEMG) activity and median power frequency in the previously injured hamstring muscle during maximal voluntary contractions. Recreational athletes were recruited, 13 with a history of unilateral hamstring strain injury and 15 without prior injury. All athletes undertook isokinetic dynamometry testing of the knee flexors and sEMG assessment of the biceps femoris long head (BF) and medial hamstrings (MHs) during concentric and eccentric contractions at ±180 and ±60°s(-1). The knee flexors on the previously injured limb were weaker at all contraction speeds compared to the uninjured limb (+180°s(-1)p=0.0036; +60°s(-1)p=0.0013; -60°s(-1)p=0.0007; -180°s(-1)p=0.0007) whilst sEMG activity was only lower in the BF during eccentric contractions (-60°s(-1)p=0.0025; -180°s(-1)p=0.0003). There were no between limb differences in MH sEMG activity or median power frequency from either BF or MH in the injured group. The uninjured group showed no between limb differences in any of the tested variables. Secondary analysis comparing the between limb difference in the injured and the uninjured groups, confirmed that previously injured hamstrings were mostly weaker (+180°s(-1)p=0.2208; +60°s(-1)p=0.0379; -60°(-1)p=0.0312; -180°s(-1)p=0.0110) and that deficits in sEMG were confined to the BF during eccentric contractions (-60°s(-1)p=0.0542; -180°s(-1)p=0.0473). Previously injured hamstrings were weaker and BF sEMG activity was lower than the contralateral uninjured hamstring. This has implications for hamstring strain injury prevention and rehabilitation which should consider altered neural function following hamstring strain injury.
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Papers by Ryan Timmins
PURPOSE: To determine the impact of fatigue induced by intermittent sprinting on the MPF of the medial and lateral hamstring muscles.
METHODS: Fifteen recreationally active males completed 18 × 20m overground sprints. Maximal strength (concentric and eccentric knee flexor and concentric knee extensor) was determined isokinetically at the velocities of ±1800.s-1 and ±600.s-1 while hamstring muscle activation was assessed using surface electromyography, before and 15 minutes after the running protocol.
RESULTS: Overground intermittent sprint running caused a significant reduction in eccentric knee flexor strength (27.2 Nm; 95% CI = 11.2 to 43.3; p=0.0001) but not concentric strength (9.3 Nm; 95% CI = -6.7 to 25.3; P=0.6361). Following intermittent sprinting, MPF of the lateral hamstrings showed a significant decline eccentrically at both -1800.s-1 (5.26; 95% CI = 0.34 to 9.84; p=0.0452) and -600.s-1(2.96; 95% CI = 0.15 to 7.54; p=0.0347). However, there was no significant decline concentrically at either speeds (p>0.05). Furthermore, there were also no significant declines in the medial hamstring MPF following intermittent sprinting (p>0.05).
CONCLUSION: Sprint running induced fatigue led to an eccentric specific reduction in knee flexor torque, as well as a decline in eccentric, lateral hamstring MPF. Furthermore, MPF was suppressed across both contraction modes for the medial hamstrings. These findings indicate that fatigue is associated with the declines in MPF of the lateral hamstrings following intermittent sprint running. However, this decline is potentially contraction mode specific, with decreases in MPF only occurring during eccentric contractions. This association between fatigue and MPF may also indicate that conduction rates and fibre type recruitment of the lateral hamstrings, during eccentric contractions may be significantly altered following sprint running.
PURPOSE: To determine the impact of fatigue induced by intermittent sprinting on the MPF of the medial and lateral hamstring muscles.
METHODS: Fifteen recreationally active males completed 18 × 20m overground sprints. Maximal strength (concentric and eccentric knee flexor and concentric knee extensor) was determined isokinetically at the velocities of ±1800.s-1 and ±600.s-1 while hamstring muscle activation was assessed using surface electromyography, before and 15 minutes after the running protocol.
RESULTS: Overground intermittent sprint running caused a significant reduction in eccentric knee flexor strength (27.2 Nm; 95% CI = 11.2 to 43.3; p=0.0001) but not concentric strength (9.3 Nm; 95% CI = -6.7 to 25.3; P=0.6361). Following intermittent sprinting, MPF of the lateral hamstrings showed a significant decline eccentrically at both -1800.s-1 (5.26; 95% CI = 0.34 to 9.84; p=0.0452) and -600.s-1(2.96; 95% CI = 0.15 to 7.54; p=0.0347). However, there was no significant decline concentrically at either speeds (p>0.05). Furthermore, there were also no significant declines in the medial hamstring MPF following intermittent sprinting (p>0.05).
CONCLUSION: Sprint running induced fatigue led to an eccentric specific reduction in knee flexor torque, as well as a decline in eccentric, lateral hamstring MPF. Furthermore, MPF was suppressed across both contraction modes for the medial hamstrings. These findings indicate that fatigue is associated with the declines in MPF of the lateral hamstrings following intermittent sprint running. However, this decline is potentially contraction mode specific, with decreases in MPF only occurring during eccentric contractions. This association between fatigue and MPF may also indicate that conduction rates and fibre type recruitment of the lateral hamstrings, during eccentric contractions may be significantly altered following sprint running.