Knee and hip joint dynamics differ between sprinting and Nordic hamstring exercises.

Sprinting places the biceps femoris long head (BFLH) at longer muscle-tendon unit lengths than the NHE across all speeds.

• Fourteen athletic participants (8 males, 6 females) were tested running at 4-8 m/s and performing the NHE.
• Motion capture, force data, and musculoskeletal modeling were used to compute joint kinematics/kinetics and estimate BFLH muscle-tendon unit length and velocity.
• Sprinting produced longer BFLH lengths than the NHE for all running speeds (p < 0.001).

Sprinting produces higher BFLH lengthening velocities than the NHE across all speeds.

• BFLH lengthening velocity was compared between the flight phase of sprinting and the NHE.
• Sprinting resulted in higher lengthening velocities than the NHE for all running speeds (p < 0.001).
• The comparison was made during the BFLH lengthening portion of the flight phase of running versus the NHE repetition.

The NHE requires smaller peak knee flexion moments than running at 6 m/s and above.

• Peak knee flexion moments during the NHE were compared to those during running across speeds from 4-8 m/s.
• NHE peak knee flexion moments were smaller than for running at 6 m/s and above (p < 0.001).
• This indicates the NHE imposes lower instantaneous knee joint loading demands compared to higher-speed running.

Peak negative knee flexion power during the NHE is less than 5% of that observed at all running speeds.

• Peak negative knee flexion power was compared between the NHE and all running speeds (4-8 m/s).
• NHE peak negative knee flexion powers were less than 5% of all running speeds (p < 0.001).
• This finding highlights a large difference in instantaneous power demands between the two modalities.

The duration of each NHE repetition is approximately 60 times longer than the BFLH lengthening portion of the flight phase of running.

• The extended duration of the NHE affects cumulative work despite lower instantaneous power.
• Because of this duration difference, negative knee work was greater for the NHE than for running at 6 m/s and below (p < 0.001).
• However, at 7.5 m/s and above, negative knee work was less for the NHE than for running (p < 0.001).

The study used musculoskeletal modeling combined with experimental motion capture and force data to compare biomechanical demands of sprinting and the NHE.

• Fourteen athletic participants (8 males, 6 females) were recruited.
• Participants ran at speeds of 4-8 m/s and performed the NHE.
• Experimental data were used in musculoskeletal modeling to compute joint kinematics and kinetics and estimate BFLH muscle-tendon unit length and velocity.
• The study was described as an exploratory analysis.