KNEE FLEXOR MUSCLE ACTIVATION AND FATIGUE DURING REPEATED NORDIC HAMSTRING EXERCISES

Y. Hiroshige¹, R. Yamaguchi², T. Ebato³, D. Watanabe⁴

¹Teikyo University, Institute of Sports Science and Medicine, Hachioji, Tokyo, Japan, ²Waseda University, Graduate School of Sport Sciences, Tokorozawa, Saitama, Japan, ³International Pacific University, Faculty of Physical Education, Okayama, Okayama, Japan, ⁴National Cerebral and Cardiovascular Center, Suita, Osaka, Japan

Background: Nordic hamstring exercise (NHE) is well known as an effective method of preventing Hamstring strain injury (HSI). However, one issue with the NHE protocol is poor compliance due to the high volume of exercise. Therefore, to optimize exercise volume, effects of NHE on muscle fatigue (decreased force) and activation (increased force) must be investigated.

Purpose: The objective of this study was to measure the changes in the eccentric tensile force of the hamstring and knee flexion angle, at which maximum tensile force was exerted, during the repeated performance of the NHE in order to identify. This would provide insight into the effective performance of the NHE for HSI prevention. For instance,
(1) the number of repetitions, at which muscle activation was greatest,
(2) number of repetitions, at which maximum tensile force was exerted at the smallest knee flexion angle, and
(3) changes in muscle activity and fatigue at different flexion angle zones.

Methods: The participants were 53 university students who were track sprinters or soccer players. They performed the NHE 10 times, and knee flexor muscle peak tensile force and knee flexion angle, at which this peak force was achieved, were compared at different times during this sequence:
phase 1, value measured during the 1st NHE;
phase 2, mean of values measured during the 2nd–4th repetitions;
phase 3, mean of values measured during the 5th–7th repetitions; and
phase 4, mean of values measured during the 8th–10th repetitions.
We also divided the knee flexor muscle peak tensile force into the knee deep flexion (90º–60º) and slight flexion (60º–30º) zones and evaluated changes in them during different phases and flexion zones.

Results: The knee flexion maximum eccentric tensile force in phase 2 was significantly higher than those in phase1, 3 and 4. The knee angle, at which maximum force was exerted, was greatest during phase 1 and decreased in phase 2 and thereafter. Interactions were also evident between the phases and deep flexion/ slight flexion zones. In terms of differences between phases in the slight flexion zone, the changes in tensile force in phase 2, 3 and 4 were all significantly greater than that in phase 1. In the deep flexion zone, there were no significant difference in the change in tensile force between phases. In terms of differences in tensile force between the deep flexion/ slight flexion zones during each phase, the value in the slight flexion zone was significantly greater than that in the deep flexion zone in phases 2 and 3.

Conclusions: As a results of monitoring knee flexor muscle activation and fatigue by repeated NHE, it was found that knee flexor muscle activation and activation in the slight flexion zone occur during a few repetitions of the NHE.

Implications: Because knee flexor muscle activation during a few repetitions of the NHE, NHE volume had better be reconsidered. Knee is often slightly flexed when HSI occurs. Therefore, knee flexion muscle activation in the similar angle zone with NHE may be a part of reason of HSI prevention.

Funding acknowledgements: This work was supported by JSPS KAKENHI Grant Number JP20K11406.

Keywords:
Nordic hamstring exercise
Muscle fatigue
Injury prevention

Topics:
Sport & sports injuries
Musculoskeletal: lower limb
Musculoskeletal

Did this work require ethics approval? Yes

Institution: International Pacific University

Committee: institutional review board

Ethics number: 20-019