The acute effects of higher versus lower load duration and intensity on morphological and mechanical properties of the healthy Achilles tendon: a randomized crossover trial

Merza, E; Pearson, SJ; Lichtwark, G; Malliaras, P

Abstract

ABSTRACT The Achilles tendon (AT) exhibits volume changes related to fluid flow under acute load which may be linked to changes in stiffness. Fluid flow provides a mechanical signal for cellular activity and may be one mechanism that facilitates tendon adaptation. This study aimed to investigate whether isometric intervention involving a high level of load duration and intensity could maximize the immediate reduction in AT volume and stiffness compared with interventions involving a lower level of load duration and intensity. Sixteen healthy participants (12 males, 4 females; age 24.4±9.4 years, body mass 70.9±16.1 kg, height 1.7±0.1 m) performed three isometric interventions of varying levels of load duration (2 s and 8 s) and intensity (35% and 75% maximal voluntary isometric contraction) over a 3 week period. Freehand 3D ultrasound was used to measure free AT volume (at rest) and length (at 35%, 55% and 75% of maximum plantarflexion force) pre- and post-interventions. The slope of the force–elongation curve over these force levels represented individual stiffness (N mm−1). Large reductions in free AT volume and stiffness resulted in response to long-duration high-intensity loading whilst less reduction was produced with a lower load intensity. In contrast, no change in free AT volume and a small increase in AT stiffness occurred with lower load duration. These findings suggest that the applied load on the AT must be heavy and sustained for a long duration to maximize immediate volume reduction, which might be an acute response that enables optimal long-term tendon adaptation via mechanotransduction pathways.

Citation

Merza, E., Pearson, S., Lichtwark, G., & Malliaras, P. (2022). The acute effects of higher versus lower load duration and intensity on morphological and mechanical properties of the healthy Achilles tendon: a randomized crossover trial. Journal of Experimental Biology, 225(10), https://doi.org/10.1242/jeb.243741

• Journal Article Type: Article
• Acceptance Date: Apr 19, 2022
• Online Publication Date: May 13, 2022
• Publication Date: May 13, 2022
• Deposit Date: Jun 15, 2022
• Publicly Available Date: Jun 15, 2022
• Journal: Journal of Experimental Biology
• Print ISSN: 0022-0949
• Publisher: Company of Biologists
• Volume: 225
• Issue: 10
• DOI: https://doi.org/10.1242/jeb.243741
• Keywords: Insect Science, Molecular Biology, Animal Science and Zoology, Aquatic Science, Physiology, Ecology, Evolution, Behavior and Systematics
• Publisher URL: https://doi.org/10.1242/jeb.243741
• Additional Information: Funders : Monash University; Projects : unspecified