Nordic Hamstring Exercise training induces improved lower‐limb swing phase mechanics and sustained strength preservation in sprinters

Abstract

Nordic Hamstring Exercise (NHE) training improves eccentric hamstring strength and sprint performance. However, detraining causes rapid reductions of achieved adaptations. Furthermore, the transfer of improved hamstring capacity to swing phase mechanics of sprints is unknown. This longitudinal study aimed (a) to quantify NHE‐induced adaptations by camera‐based isokinetic assessments and sprint analyses, (b) to relate the magnitude of adaptations to the participants' initial performance level, (c) to investigate the transferability to sprints, and (4) to determine strength preservations after 3 months. Twelve sprinters (21 years, 1.81 m, 74 kg) were analyzed throughout 22 weeks. They performed maximal sprints and eccentric knee flexor and concentric knee extensor tests before and after a 4‐week NHE training. Sprints and isokinetic tests were captured by ten and four high‐speed cameras. The dynamic control ratio at the equilibrium point (DCRe) evaluated thigh muscle balance. High‐intensity NHE training elicited significant improvements of hamstring function (P range: <.001‐.011, d range: 0.44‐1.14), thigh muscle balance (P < 0.001, d range: 0.80‐1.08) and hamstring‐related parameters of swing phase mechanics (P range: <0.001‐0.022, d range: 0.12‐0.57). Sprint velocity demonstrated small increases (+1.4%, P < 0.001, d = 0.26). Adaptations of hamstring function and thigh muscle balance revealed moderate to strong transfers to improved sprint mechanics (P range: <0.001‐0.048, R2 range: 34%‐83%). The weakest participants demonstrated the highest adaptations of isokinetic parameters (P range: 0.003‐0.023, R2 range: 42%‐62%), whereas sprint mechanics showed no effect of initial performance level. Three months after the intervention, hamstring function (+6% to +14%) and thigh muscle balance (+8% to +10%) remained significantly enhanced (P < 0.001, ƞp2 range: 0.529‐0.621). High‐intensity NHE training induced sustained improved hamstring function of sprinters, which can be transferred to swing phase mechanics of maximal sprints. The initial performance level, NHE training procedures and periodization should be considered to optimize adaptations.

The ANHEQ Evaluation Criteria: Introducing Reliable Rating Scales for Assessing Nordic Hamstring Exercise Quality

“…Therefore, it is recommended that a monitor provides an explicit position at each instance (angle–time information) in real time to the participants (Fig. 2 a, b) [ 9 , 10 , 14 , 21 ]. It is advised to present continuous information during the exercise where the participant's body should be situated at every single point in time.…”

“…Prospective NHE interventions should determine individual relationships between training loads and performance as well as related physical parameters to recognize responders and non-responders [ 35 ]. Finally, the transfer of NHE-induced improved hamstring strength to sport-specific tasks such as sprinting is of major interest [ 14 ]. But most importantly, future NHE assessments as well as interventions should be conducted according to the ANHEQ criteria to allow better replication and understanding of study quality.…”

“…However, special emphasis should always be directed toward the activation and time under tension at injury-relevant longer muscle lengths [ 1 , 2 , 5 , 6 ]. Due to the well-demonstrated positive effects of eccentric movements, the high physical demands and the fatiguing character of NHEs, it is advised to perform just the descent part of the NHE in an active fashion [ 9 , 10 , 12 , 14 , 24 ].…”

“…NHE assessments and interventions on specific devices [ 6 , 17 , 21 , 22 ] or isometric dynamometers [ 9 , 10 , 14 ] (Fig. 2 a, b) are recommended to quantify exercise determinants, performance parameters and exercise quality.…”

“…Assisted NHE execution—e.g., provided by a partner being located in front of the athlete and adjusting the pressure of his hands to the athlete’s shoulders according to the respective movement velocity (Fig. 1 b) or by means of an elastic band [ 13 , 15 , 16 ]—is recommended to acquire proper exercise quality, to reduce the fear of uncontrolled falling and to increase the actively controlled range of motion, especially within early training stages of inexperienced athletes or patients [ 9 , 10 , 13 , 14 ].…”