Hamstrings Volumetric Adaptations to a Four-Week Nordic Hamstring Exercise Protocol in Individuals with ACL...

Area of Science:

• Orthopedics
• Sports Medicine
• Rehabilitation Science

Background:

• Hamstring atrophy is common after anterior cruciate ligament reconstruction (ACLR) using hamstring tendon (HT) autografts.
• Nordic hamstring exercise (NHE) is known to increase hamstring volume in healthy individuals, but its effect post-ACLR is unstudied.

Purpose of the Study:

• To investigate changes in hamstring muscle volumes following an isolated NHE protocol in individuals who have undergone ACLR with HT autograft.

Main Methods:

• A prospective case series involving seven participants (age 18-35) with unilateral ACLR via HT.
• Muscle volumes of the hamstrings were measured using MRI before and after a four-week, 10-session NHE protocol.
• Peak eccentric force was measured using a NordBord dynamometer.

Main Results:

• Hamstring muscle volumes showed variable changes (-6.0% to 17.6%), with average increases of 3.3-7.2% (Cohen's d=0.12-0.53) for most muscles, except the semimembranosus (0.0%).
• Average peak eccentric force increased by 11.0% (Cohen's d=0.53).

Conclusions:

• Isolated NHE led to trivial-to-moderate increases in hamstring muscle volumes and moderate increases in eccentric force in the majority of participants post-ACLR.
• The varied individual responses highlight the need for tailored exercise prescriptions in this patient population.