Maximum dorsiflexion increases Achilles tendon force during exercise for midportion Achilles tendinopathy

Area of Science:

• Biomechanics
• Sports Medicine
• Rehabilitation Science

Background:

• Non-insertional Achilles tendinopathy rehabilitation often utilizes eccentric loading (ECC) exercises.
• The mechanical principles behind ECC effectiveness remain unclear, prompting investigation into alternative protocols like heavy slow resistance (HSR) loading.
• HSR has demonstrated comparable outcomes to ECC with reduced training duration.

Purpose of the Study:

• To investigate the impact of external loading and other variables on Achilles tendon (AT) force during ECC and HSR exercises.
• To compare the mechanical demands placed on the AT between ECC and HSR protocols.
• To identify key factors influencing AT force to optimize rehabilitation strategies.

Main Methods:

• Collected ground reaction force and kinematic data from 18 healthy participants under four loading conditions.
• Estimated AT moment arms using MRI data from each participant.
• Calculated AT force via inverse dynamics using ankle torque derived from collected data.

Main Results:

• Achilles tendon force was not greater in the eccentric phase compared to the concentric phase for both ECC and HSR.
• Under identical external loads, ECC with a bent knee generated higher AT force than HSR with a straight knee, attributed to greater ankle dorsiflexion.
• Multivariate regression identified external load and maximum dorsiflexion angle as significant predictors of peak AT force.

Conclusions:

• Rehabilitation exercises should incorporate sufficient external load and achieve maximum dorsiflexion to effectively load the Achilles tendon.
• Standing exercises may be more effective than seated variations for the same external load and peak dorsiflexion due to a greater influence of dorsiflexion angle on AT force.
• These findings provide mechanical insights to optimize exercise selection and execution for Achilles tendinopathy rehabilitation.