What question did this study set out to answer?

The research aims to quantify the energy cost of muscle contractions at varying muscle-tendon unit lengths.

March 1, 2026Open Access

The energy cost of cyclic muscle contractions at different initial muscle-tendon unit lengths derived from near-infrared spectroscopy

Key Result

Cyclic contractions at 0.85Lo increased medial gastrocnemius energy cost by 36% and muscle activity twofold, indicating higher cost per force due to lower initial muscle length.

Key Points

The research aims to quantify the energy cost of muscle contractions at varying muscle-tendon unit lengths.
Participants performed 30 submaximal fixed-end contractions at 0.85Lo, Lo, and 1.15Lo in random order.
Energy cost was measured using near-infrared spectroscopy during blood flow occlusion.
EMG was used to quantify medial gastrocnemius muscle activity.
Forced measurements and shortening dynamics were compared across muscle-tendon unit lengths.
Energy cost was 36% higher at 0.85Lo compared to Lo (P = 0.005).
At 1.15Lo, energy cost was similar to Lo, indicating a balance despite lower force at 0.85Lo.
Muscle activity was roughly twice as high at 0.85Lo (P = 0.001).
The energy cost per unit force was significantly elevated at 0.85Lo compared to Lo and 1.15Lo (P = 0.008).

Structured PICO

Population

Human participants

Intervention

30 submaximal fixed-end contractions at an ankle joint angle associated with 0.85Lo and 1.15Lo

Comparator

Contractions at optimal length (Lo)

Outcome

Energy cost (EC) of the medial gastrocnemius muscle quantified from near-infrared spectroscopy during blood flow occlusionsurrogate

Cyclic muscle contractions at short initial muscle-tendon unit lengths have a significantly higher energy cost due to lower force potential.

Main Result

Absolute Event Rate: 0% vs 0%

Abstract

During locomotion, the plantarflexor muscle fascicles appear to operate on the ascending limb of its maximal force-length relationship, producing less force per unit activation and elevating the energy cost (EC) compared with contractions performed at optimal length (Lo). The EC of the medial gastrocnemius muscle was quantified at different initial muscle-tendon unit lengths by having participants perform 30 submaximal fixed-end contractions at an ankle joint angle associated with 0.85Lo, Lo, and 1.15Lo in a random order, cyclically targeting 50% of the maximal force at 0.85Lo. EC was quantified from near-infrared spectroscopy during blood flow occlusion and EMG quantified MG muscle activity. Mean EC was 36 ± 24% higher at 0.85Lo (P = 0.005) compared with Lo. Mean EC at 1.15Lo (2 ± 27% lower) was similar to that at Lo (P = 0.81), despite lower forces at 0.85Lo (P = 0.02), and similar absolute fascicle shortening (P = 0.10), and shortening velocity (P = 0.52). Muscle activity was approximately twofold higher at 0.85Lo (P = 0.001). The EC per unit activation was similar across lengths (P = 0.45), whereas the EC per unit force was significantly higher at 0.85Lo compared with Lo and 1.15Lo (P = 0.008). Together, these results demonstrate a significant increase in the cost of cyclically producing force at short initial muscle-tendon unit lengths, due to a lower force potential at that initial muscle fascicle length, which we surmise is a result of a lower cross-bridge force and not a higher energetic cost of activation.