Ryan Timmins

Eccentric Hamstring Strength and Hamstring Injury Risk in Australian Footballers

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.

Short biceps femoris fascicles and eccentric knee flexor weakness increase the risk of hamstring injury in elite football (soccer): a prospective cohort study

Background/aim 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). Methods 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. Results 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. Conclusions 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.

Biceps femoris long head architecture: A reliability and retrospective injury study

PURPOSE This study aimed (i) to determine the reliability of two-dimensional ultrasonography for the assessment of biceps femoris long head (BFlh) architectural characteristics and (ii) to determine whether limbs with a history of strain injury in the BFlh display different architecture and eccentric strength compared to uninjured limbs. METHODS This case-control study (control [n = 20], injured group [n = 16], males) assessed the BFlh architecture at rest and during graded isometric contractions using two-dimensional ultrasonography. The control group were assessed three times (>24 h apart) to determine reliability. Previously injured individuals were evaluated once. RESULTS The assessment of BFlh architecture was highly reliable (intraclass correlations >0.90). Fascicle length (P < 0.001; d range = 0.67-1.34) and fascicle length relative to muscle thickness (P < 0.001; d range = 0.58-0.85) of the previously injured BFlh were significantly less than the contralateral uninjured BFlh at all intensities. Pennation angle of the previously injured BFlh was significantly greater (P < 0.001; d range = 0.62-0.88) than the contralateral uninjured BFlh at all intensities. Eccentric strength in the previously injured limb was significantly lower than that in the contralateral limb (-15.4%; -52.5 N, 95% confidence interval = -76.2 to -28.4; P < 0.001, d = 0.56). CONCLUSIONS These data indicate that two-dimensional ultrasonography is reliable for assessing BFlh architecture at rest and during graded isometric contractions. Fascicle length, fascicle length relative to muscle thickness, and pennation angle are significantly different in previously injured BFlh compared to an uninjured contralateral BFlh. Eccentric strength of the previously injured limb is also significantly lower than that of the uninjured contralateral limb. These findings have implications for rehabilitation and injury prevention practices, which should consider altered architectural characteristics.

Architectural Changes of the Biceps Femoris Long Head after Concentric or Eccentric Training.

PURPOSE To determine the architectural adaptations of the biceps femoris long head (BFlh) after concentric or eccentric strength training interventions and the time course of adaptation during training and detraining. METHODS Participants in this intervention (concentric training group [n = 14], eccentric training group [n = 14], male subjects) completed a 4-wk control period, followed by 6 wk of either concentric- or eccentric-only knee flexor training on an isokinetic dynamometer and finished with 28 d of detraining. Architectural characteristics of BFlh were assessed at rest and during graded isometric contractions using two-dimensional ultrasonography at 28 d prebaseline; baseline; and days 14, 21, and 42 of the intervention and then again after 28 d of detraining. RESULTS BFlh fascicle length was significantly longer in the eccentric training group (P < 0.05; d range, 2.65-2.98) and shorter in the concentric training group (P < 0.05; d range, -1.62 to -0.96) after 42 d of training compared with baseline at all isometric contraction intensities. After the 28-d detraining period, BFlh fascicle length was significantly reduced in the eccentric training group at all contraction intensities compared with the end of the intervention (P < 0.05; d range, -1.73 to -1.55). There was no significant change in fascicle length of the concentric training group after the detraining period. CONCLUSIONS These results provide evidence that short-term resistance training can lead to architectural alterations in the BFlh. In addition, the eccentric training-induced lengthening of BFlh fascicle length was reversed and returned to baseline values after 28 d of detraining. The contraction mode specific adaptations in this study may have implications for injury prevention and rehabilitation.

Rate of Torque and Electromyographic Development During Anticipated Eccentric Contraction Is Lower in Previously Strained Hamstrings

Background: The effect of prior strain injury on myoelectrical activity of the hamstrings during tasks requiring high rates of torque development has received little attention. Purpose: To determine if recreational athletes with a history of unilateral hamstring strain injury will exhibit lower levels of myoelectrical activity during eccentric contraction, rate of torque development (RTD), and impulse (IMP) at 30, 50, and 100 milliseconds after the onset of myoelectrical activity or torque development in the previously injured limb compared with the uninjured limb. Study Design: Case control study; Level of evidence, 3. Methods: Twenty-six recreational athletes were recruited. Of these, 13 athletes had a history of unilateral hamstring strain injury (all confined to biceps femoris long head), and 13 had no history of hamstring strain injury. Following familiarization, all athletes undertook isokinetic dynamometry testing and surface electromyography (integrated EMG; iEMG) assessment of the biceps femoris long head and medial hamstrings during eccentric contractions at −60 and −180 deg·s−1. Results: In the injured limb of the injured group, compared with the contralateral uninjured limb, RTD and IMP was lower during −60 deg·s−1 eccentric contractions at 50 milliseconds (RTD: injured limb, 312.27 ± 191.78 N·m·s−1 vs uninjured limb, 518.54 ± 172.81 N·m·s−1, P = .008; IMP: injured limb, 0.73 ± 0.30 N·m·s vs uninjured limb, 0.97 ± 0.23 N·m·s, P = .005) and 100 milliseconds (RTD: injured limb, 280.03 ± 131.42 N·m·s−1 vs uninjured limb, 460.54 ± 152.94 N·m·s−1, P = .001; IMP: injured limb, 2.15 ± 0.89 N·m·s vs uninjured limb, 3.07 ± 0.63 N·m·s, P < .001) after the onset of contraction. Biceps femoris long head muscle activation was lower at 100 milliseconds at both contraction speeds (–60 deg·s−1, normalized iEMG activity [×1000]: injured limb, 26.25 ± 10.11 vs uninjured limb, 33.57 ± 8.29, P = .009; –180 deg·s−1, normalized iEMG activity [×1000]: injured limb, 31.16 ± 10.01 vs uninjured limb, 39.64 ± 8.36, P = .009). Medial hamstring activation did not differ between limbs in the injured group. Comparisons in the uninjured group showed no significant between limbs difference for any variables. Conclusion: Previously injured hamstrings displayed lower RTD and IMP during slow maximal eccentric contraction compared with the contralateral uninjured limb. Lower myoelectrical activity was confined to the biceps femoris long head. Regardless of whether these deficits are the cause of or the result of injury, these findings could have important implications for hamstring strain injury and reinjury. Particularly, given the importance of high levels of muscle activity to bring about specific muscular adaptations, lower levels of myoelectrical activity may limit the adaptive response to rehabilitation interventions and suggest that greater attention be given to neural function of the knee flexors after hamstring strain injury.

Impact of the Nordic hamstring and hip extension exercises on hamstring architecture and morphology: implications for injury prevention

Background The architectural and morphological adaptations of the hamstrings in response to training with different exercises have not been explored. Purpose To evaluate changes in biceps femoris long head (BFLH) fascicle length and hamstring muscle size following 10-weeks of Nordic hamstring exercise (NHE) or hip extension (HE) training. Methods 30 recreationally active male athletes (age, 22.0±3.6 years; height, 180.4±7 cm; weight, 80.8±11.1 kg) were allocated to 1 of 3 groups: (1) HE training (n=10), NHE training (n=10), or no training (control, CON) (n=10). BFLH fascicle length was assessed before, during (Week 5) and after the intervention with a two-dimensional ultrasound. Hamstring muscle size was determined before and after training via MRI. Results Compared with baseline, BFLH fascicles were lengthened in the NHE and HE groups at mid-training (d=1.12–1.39, p<0.001) and post-training (d=1.77–2.17, p<0.001) and these changes did not differ significantly between exercises (d=0.49–0.80, p=0.279–0.976). BFLH volume increased more for the HE than the NHE (d=1.03, p=0.037) and CON (d=2.24, p<0.001) groups. Compared with the CON group, both exercises induced significant increases in semitendinosus volume (d=2.16–2.50, ≤0.002) and these increases were not significantly different (d=0.69, p=0.239). Conclusion NHE and HE training both stimulate significant increases in BFLH fascicle length; however, HE training may be more effective for promoting hypertrophy in the BFLH.

Architectural adaptations of muscle to training and injury: a narrative review outlining the contributions by fascicle length, pennation angle and muscle thickness

Background 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. Objectives 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 architectural alterations following training interventions, immobilisation and injury have on force production and (3) present a hypothesis on how neuromuscular inhibition could cause maladaptations to muscle architecture following injury.

The Effect of Previous Hamstring Strain Injuries on the Change in Eccentric Hamstring Strength During Preseason Training in Elite Australian Footballers

Background: 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. Purpose: 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). Study Design: Cohort study; Level of evidence, 2. Methods: 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 normalized to the start of preseason strength. The start of preseason strength was used as a covariate to control for differences in starting strength. Results: The left and right limbs in the control group showed no difference in absolute or relative change (left limb: 60.7 ± 72.9 N and 1.28 ± 0.34 N, respectively; right limb: 48.6 ± 83.8 N and 1.24 ± 0.43 N, respectively). Similarly, the injured and uninjured limbs in the previously injured group showed no difference in either absolute or relative change (injured limb: 13.1 ± 57.7 N and 1.07 ± 0.18 N, respectively; uninjured limb: 14.7 ± 54.0 N and 1.07 ± 0.22 N, respectively). The previously injured group displayed significantly less increase in eccentric hamstring strength across the preseason (absolute change, 13.9 ± 55.0 N; relative change, 1.07 ± 0.20 N) compared with the control group (absolute change, 54.6 ± 78.5 N; relative change, 1.26 ± 0.39 N) for both absolute and relative measures (P < .001), even after controlling for differences in the start of preseason eccentric hamstring strength, which had a significant effect on strength improvement. Conclusion: Elite Australian footballers with a unilateral history of HSIs displayed less improvement in eccentric hamstring strength across preseason training. The smaller improvements were not restricted to the previously injured limb as the contralateral limb also displayed similarly small improvements in eccentric strength. Whether this is the cause of or the result of an injury remains to be seen, but it has the potential to contribute to the risk of hamstring strain reinjuries.

Hamstring strength and flexibility after hamstring strain injury: a systematic review and meta-analysis

Objective To systematically review the evidence base related to hamstring strength and flexibility in previously injured hamstrings. Design Systematic review and meta-analysis. Data sources A systematic literature search was conducted of PubMed, CINAHL, SPORTDiscus, Cochrane Library, Web of Science and EMBASE from inception to August 2015. Inclusion criteria 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. Results 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 isokinetically measured concentric (60°/s, d=−0.33) and Nordic eccentric knee flexor strength (d=−0.39). The conventional hamstring to quadricep strength ratios were also reduced well after return to play (60:60°/s, d=−0.32; 240:240°/s, d=−0.43) and functional (30:240°/s, d=−0.88), but these effects were inconsistent across measurement methods. Conclusions After hamstring strain, acute isometric and passive straight leg raise deficits resolve within 20–50 days. Deficits in eccentric and concentric strength and strength ratios persist after return to play, but this effect was inconsistent across measurement methods. Flexibility and isometric strength should be monitored throughout rehabilitation, but dynamic strength should be assessed at and following return to play.

Biceps Femoris Architecture and Strength in Athletes with a Previous Anterior Cruciate Ligament Reconstruction.

PURPOSE This study aimed to determine whether limbs with a history of anterior cruciate ligament (ACL) injury reconstructed from the semitendinosus display different biceps femoris long head (BFlh) architecture and eccentric strength, assessed during the Nordic hamstring exercise, compared with the contralateral uninjured limb. METHODS The architectural characteristics of the BFlh were assessed at rest and at 25% of a maximal voluntary isometric contraction (MVIC) in the control group (n = 52) and in the group who had previous ACL injury (n = 15) using two-dimensional ultrasonography. Eccentric knee flexor strength was assessed during the Nordic hamstring exercise. RESULTS Fascicle length was shorter (P = 0.001; d range, 0.90-1.31) and pennation angle (P range, 0.001-0.006; d range, 0.87-0.93) was greater in the BFlh of the ACL-injured limb compared with those in the contralateral uninjured limb at rest and during a 25% MVIC. Eccentric strength was lower in the ACL-injured limb when compared with the contralateral uninjured limb. Fascicle length, MVIC, and eccentric strength were not different between the left and right limb in the control group. CONCLUSIONS Limbs with a history of ACL injury reconstructed from the semitendinosus have shorter fascicles and greater pennation angles in the BFlh compared with those of the contralateral uninjured side. Eccentric strength during the Nordic hamstring exercise of the ACL-injured limb is significantly lower than that of the contralateral side. These findings have implications for ACL rehabilitation and hamstring injury prevention practices, which should consider altered architectural characteristics.