The effect of Nordic hamstring exercise training volume on biceps femoris long head architectural adaptation.

The aim of this study was to determine the time course of architectural adaptations in the biceps femoris long head (BFLH ) following high or low volume eccentric training. Twenty recreationally active males completed a two week standardized period of eccentric Nordic hamstring exercise (NHE) training, followed by four weeks of high (n = 10) or low volume (n = 10) training. Eccentric strength was assessed pre- and post intervention and following detraining. Architecture was assessed weekly during training and after two and four weeks of detraining. After six weeks of training, BFLH fascicles increased significantly in the high (23% ± 7%, P < .001, d = 2.87) and low volume (24% ± 4%, P < .001, d = 3.46) groups, but reversed following two weeks of detraining (high volume: -17% ± 5%, P < .001, d = -2.04; low volume: -15% ± 3%, P < .001, d = -2.56) after completing the intervention. Both groups increased eccentric strength after six weeks of training (high volume: 28% ± 20%, P = .009, d = 1.55; low volume: 34% ± 14%, P < .001, d = 2.09) and saw no change in strength following a four week period of detraining (high volume: -7% ± 7%, P = .97, d = -0.31; low volume: -2% ± 5%, P = .99, d = -0.20). Both low and high volume NHE training stimulate increases in BFLH fascicle length and eccentric knee flexor strength. Architectural adaptations reverted to baseline levels within two weeks after ceasing training, but eccentric strength was maintained for at least four weeks. These observations provide novel insight into the effects of training volume and detraining on BFLH architecture and may provide guidance for the implementation of NHE programs.

Muscle activation patterns in the Nordic hamstring exercise: Impact of prior strain injury.

This study aimed to determine: (a) the spatial patterns of hamstring activation during the Nordic hamstring exercise (NHE); (b) whether previously injured hamstrings display activation deficits during the NHE; and (c) whether previously injured hamstrings exhibit altered cross-sectional area (CSA). Ten healthy, recreationally active men with a history of unilateral hamstring strain injury underwent functional magnetic resonance imaging of their thighs before and after six sets of 10 repetitions of the NHE. Transverse (T2) relaxation times of all hamstring muscles [biceps femoris long head (BFlh); biceps femoris short head (BFsh); semitendinosus (ST); semimembranosus (SM)] were measured at rest and immediately after the NHE and CSA was measured at rest. For the uninjured limb, the ST's percentage increase in T2 with exercise was 16.8%, 15.8%, and 20.2% greater than the increases exhibited by the BFlh, BFsh, and SM, respectively (P < 0.002 for all). Previously injured hamstring muscles (n = 10) displayed significantly smaller increases in T2 post-exercise than the homonymous muscles in the uninjured contralateral limb (mean difference -7.2%, P = 0.001). No muscles displayed significant between-limb differences in CSA. During the NHE, the ST is preferentially activated and previously injured hamstring muscles display chronic activation deficits compared with uninjured contralateral muscles.

Reduced biceps femoris myoelectrical activity influences eccentric knee flexor weakness after repeat sprint running.

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 < 0.001; concentric 11 ± 2 Nm, 10% P < 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.

Acute hamstring strain injury in track-and-field athletes: A 3-year observational study at the Penn Relay Carnival.

This study aimed to observe the incidence rates of hamstring strain injuries (HSIs) across different competition levels and ages during the Penn Relays Carnival. Over a 3-year period, all injuries treated by the medical staff were recorded. The type of injury, anatomic location, event in which the injury occurred, competition level, and demographic data were documented. Absolute and relative HSI (per 1000 participants) were determined, and odds ratios (ORs) were calculated between sexes, competition levels, and events. Throughout the study period 48,473 athletes registered to participate in the Penn Relays Carnival, with 118 HSIs treated by the medical team. High school girls displayed lesser risk of HSI than high school boys (OR = 0.55, P = 0.021), and masters athletes were more likely than high school- (OR = 4.26, P < 0.001) and college-level (OR = 3.55, P = 0.001) athletes to suffer HSI. The 4 × 400-m relay displayed a greater likelihood of HSI compared with the 4 × 100-m relay (OR = 1.77, P = 0.008). High school boys and masters-level athletes are most likely to suffer HSI, and there is higher risk in 400-m events compared with 100-m events.