Author(s): GREEN, A., HAJAT, A., SOLOMONS, T.B., Institution: UNIVERSITY OF JOHANNESBURG, Country: SOUTH AFRICA, Abstract-ID: 2400

INTRODUCTION:
Muscle architecture is closely related to muscle function [1]. That is, muscle fibre arrangement can change to force or velocity dominant positions. While these chronic training adaptations are well known, the acute effect of fatigue on pennation angle remains inconclusive. The aim of this study was to evaluate pennation angle changes following a dorsiflexion specific fatigue intervention
METHODS:
Twenty-six healthy recreational athletes (Body stature: 168.9 ± 9.5cm; mass: 66.3 ± 9.8kg) volunteered for the study. were recorded. An isometric fatiguing intervention was applied where participants were required to produce maximal dorsiflex force a duration of 20 seconds across three repetitions. This was repeated over 4 sets and isometric dorsiflexion forces were measured using a VALD DynaMo. Isokinetic dorsiflexion peak power and Countermovement jump (CMJ) heights were evaluated prior to and following the fatiguing protocol. Finally, ultrasonography evaluated the tibialis anterior, lateral and medial gastrocnemius pennation angles, before and after the first isometric and isokinetic attempts. Ultrasonography was also measured after the second to fourth isometric attempts, second isokinetic attempt and CMJ heights. Paired data were analysed using Wilcoxon signed ranked and Friedman’s tests in SPSS 30, with p<0.05.
RESULTS:
Isometric dorsiflexion force differences (p>0.001) were noted between attempts 1 (292.54 ± 65.23 N) and 2 (278.00 ± 64.27N), 1 and 3 (270.65 ± 93.14 N), and 1 and 4 (263.85 ± 79.74N). Additionally, Isokinetic peak power declined (34.68 ± 13.09 vs 16.40 ± 5.74 W; p<0.001). However, no difference in CMJ height (30.58 ± 7.98 vs 31.17 ± 8.54 cm; p=0.382). Specific to muscle architecture, pennation angle of the tibialis anterior (p= 0.786; lateral gastrocnemius p=0.833; medial gastrocnemius p=0.271) all remained statistically unchanged.
CONCLUSION:
While the isometric fatigue protocol of the dorsiflexors was effective, it seems the pennation angles of the tibialis anterior and gastrocnemius remain unaffected. It is likely that muscle fibres maintain their orientation following a bout of acute isometric fatigue. The effects of eccentric and concentric actions may alter the pennation angles due to the greater range of motion required during the joint movement. Indeed, pennation angle is known to change following movements like squats [2], [3].
References
1. Sekir et al. (2019). Effects of Static and Dynamic Stretching on Muscle Architecture. Turk J Sports Med, 54(3):158.
2. Vieira et al. (2018). Acute changes in muscle thickness and pennation angle in response to work-matched concentric and eccentric isokinetic exercise. Appl Physio, Nut Metabol, 43(10): 1069.
3. Coenning et al. (2024). Impact of contraction intensity and ankle joint angle on calf muscle fascicle length and pennation angle during isometric and dynamic contractions. Sci Reports, 14:24929.