Validation of a dynamic local muscle function test and its response to local muscle temperature

Abstract

Current single joint isometric and isokinetic tests used to assess muscular performance are limited by the very testing-condition specific nature of the results, leading to a low to moderate correlation to in-vivo performance during sprinting and jumping. This study aimed to develop a single-joint plantarflexor test consisting of 30 s of maximal repeated dynamic contractions from 5° of dorsiflexion through 30° of plantarflexion at 70% of pre-testing isometric MVC. Twelve recreationally active healthy volunteers (9 male, 3 female) completed two different visits where they performed the isotonic plantarflexion test (IPFT). Session 1 aimed to establish its repeatability and variability during thermoneutral muscle temperature (36.6 ± 0.3°C). Across 4 bouts of IPFT with 30 min separation, no significant differences or pairwise differences were observed across measures of power, torque, work completed, time-to-peak torque or rate of torque development while average measures intraclass correlations ranged from 0.935 – 0.996. Session 2 assessed the sensitivity of the test to passive heating and cooling of the lower leg across thermoneutral (TN, 36.5 ± 0.3°C) Hot (38.3 ± 0.2°C) and Cold (33.3 ± 1.2°C) muscle temperatures. Aside from peak torque Hot had no effect on IPFT performance compared to TN, while Cold had a differential effect on IPFT performance. Compared to TN Cold led to significant increases in time-to-peak torque (Δ ↑ 0.14 s) and decreases in total work (Δ ↓ 10.02 J), average power (Δ ↓ 16.92 W) number of repetitions completed (Δ ↓ 4.90), average rate of torque development (Δ ↓ 65.30 Nm∙s-1) and peak torque (Δ ↓ 6.40 Nm). Changes in performance in Cold were likely due to the effects of cooling on rate processes and contractile characteristics, while we may not have heated muscle enough to impact performance in Hot. Keywords: Isotonic Plantarflexion Test, Muscle Temperature, Muscular Power, Performance