The Effects of the Leg Position on the Nordic Hamstring Exercise Eccentric Force: A Randomized Cross-Over Study.

Area of Science:

• Biomechanics
• Exercise Physiology
• Sports Science

Background:

• Hamstring recruitment is influenced by tibial positioning, particularly during eccentric contractions.
• Previous research primarily focused on concentric or isometric hamstring strength, leaving eccentric strength patterns less understood.
• Understanding hamstring activation during exercises like the Nordic hamstring is crucial for training and injury prevention.

Purpose of the Study:

• To investigate the electromyographic (EMG) response of hamstring muscles (biceps femoris and semitendinosus) during the Nordic hamstring exercise.
• To compare muscle activation across three distinct tibial positions: internal rotation, external rotation, and neutral.
• To determine if tibial rotation significantly alters hamstring recruitment patterns during eccentric loading.

Main Methods:

• A randomized crossover study design was employed.
• Surface electromyography (sEMG) was used to measure muscle activity.
• Participants performed the Nordic hamstring exercise in three randomized leg positions (internal rotation, external rotation, neutral).

Main Results:

• No statistically significant differences in hamstring muscle activation were observed between the three leg positions or sides (p > 0.05).
• Small effect sizes were noted for the biceps femoris muscle across different positions (η² = 0.01–0.03).
• The internal rotation position tended to show higher overall muscle activations, with the biceps femoris consistently showing greater activation than the semitendinosus, especially in internal rotation.

Conclusions:

• While tibial rotation may influence hamstring recruitment patterns during the Nordic hamstring exercise, the effect on eccentric strength was less pronounced than anticipated.
• The biceps femoris appears to be more activated than the semitendinosus, particularly in the internal rotation position.
• Further research may be needed to explore the nuances of hamstring activation and tibial positioning in eccentric exercises.