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

Abstract

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 exercise selection on hamstring muscle activation

“…We have previously shown that recreationally active young men with a history of unilateral hamstring strain exhibited less T2 change in previously injured muscles than in their uninjured homologous muscles from the contralateral limb after performing the Nordic exercise 22. Therefore, more research will be needed to establish whether the patterns of selective muscle activation observed in the current study are also evident in athletes with a history of strain injury 10 11 44 53. Last, it should be acknowledged that the T2 response to an exercise stimulus is highly dynamic and can be influenced by a range of factors, such as the metabolic capacity and vascular dynamics of the active tissue 28 36.…”

“…For example, inhibition of previously injured BF muscles during eccentric actions has been reported many months after rehabilitation,10 11 44 and it has been proposed45 that these deficits might partly explain observations of persistent eccentric knee flexor weakness,10 BF LongHead atrophy12 and a chronic shortening of BF LongHead fascicles 46. These data10–12 44 46 are consistent with the possibility that conventional rehabilitation strategies may not adequately target the commonly injured BF LongHead . The ratio of lateral to medial hamstring (BF/MH) nEMG varies with foot rotation47 and differs between exercises 25.…”

Biceps Femoris Long Head Architecture

“…Power was set at 80%, with an a level of 0.05, returning a calculated sample size of 15. As a cross-reference to confirm this sample size calculation, previous studies that have used similar designs have used sample sizes from 13 to 15 (26,27,34).…”

“…Retrospective reports have identified prolonged deficits in the rate o f torque develop ment (27), biceps femoris (BF) activation (26,34), BF muscle volume (33), changes in the angle o f peak torque (6), and eccentric knee flexor strength (26) when tested via isokinetic dynamometry (26) as well as during the perfonnance o f the Nordic hamstring exercise (25) in previously injured ham strings. Shifts in the angle o f peak torque toward shorter muscle lengths have been proposed to be indicative o f a reduction o f in-series sarcomeres and muscle fascicle length (6).…”

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

“…Reduced activation of previously injured hamstrings has been associated with maximal eccentric contractions,29 30 48 76 particularly at long muscle lengths 29 48. What remains to be seen, however, is whether or not these deficits are associated with increased risk of injury or reinjury, and what the most appropriate intervention is to ameliorate these deficits.…”