Influence of isometric training at short and long muscle‐tendon unit lengths on the history dependence of force

Abstract

Active muscle shortening and lengthening are prevalent in all sports, and when these motions precede an isometric (ie, constant muscle-tendon unit length) contraction, they influence force production. Specifically, the amount of force produced in an isometric steady-state is less following active shortening (residual force depression; rFD) and more following active lengthening (residual force enhancement; rFE) than a purely isometric contraction at the same muscle length and level of activation. Together, rFD and rFE encompass the intrinsic property of muscle known as the history dependence of force. 1 Since the initial discovery of the history dependence of force by Abbott and Aubert in 1952, 1 rFD and rFE have been observed in single sarcomeres, 2 single human muscle fibers, 3 and humans in vivo during submaximal and maximal contraction intensities. 4-6 The modifiability of the history dependence of force through training has recently become an area of interest: if rFD can be decreased and rFE increased, there is potential to optimize sport performance. 7-10 However, no definitive conclusions have been

Modifiability of residual force depression in single muscle fibers following uphill and downhill training in rats

“…Our findings are consistent with the literature as previous studies investigating the modifiability of rFD at the in‐vivo whole human level, and in‐vitro whole muscle level also noted that rFD was not modifiable through training (Chen et al, 2020; Chen & Power, 2019; Hinks et al, 2020). By investigating this property at the single fiber level, we are able to identify that rFD is not intrinsically modifiable at the cellular level, at least given the constraints of the current experimental design.…”

“…Training could potentially modify rFD by increasing single muscle fiber force production capacity and thus work of shortening. The only studies that have investigated the chronic modifiability of rFD following training were two in‐vivo studies testing humans (Chen & Power, 2019; Hinks et al, 2020), and an in‐vitro study in rodents (Chen et al, 2020). rFD of the ankle dorsiflexors was not modifiable at the whole human level following 4 weeks of concentric and eccentric resistance training (Chen & Power, 2019), nor 8 weeks of isometric training biased to a long or short muscle tendon unit length (Hinks et al, 2020).…”

“…The only studies that have investigated the chronic modifiability of rFD following training were two in‐vivo studies testing humans (Chen & Power, 2019; Hinks et al, 2020), and an in‐vitro study in rodents (Chen et al, 2020). rFD of the ankle dorsiflexors was not modifiable at the whole human level following 4 weeks of concentric and eccentric resistance training (Chen & Power, 2019), nor 8 weeks of isometric training biased to a long or short muscle tendon unit length (Hinks et al, 2020). Similarly, rFD does not seem to be modifiable for the SOL and EDL following uphill and downhill training in rats despite the marked difference between the uphill and downhill groups for serial sarcomere number, respectively (Chen et al, 2020).…”

Residual Force Enhancement Is Present in Consecutive Post-Stretch Isometric Contractions of the Hamstrings during a Training Simulation

“…Therefore, based on the findings of this study, future research should test the efficacy of the chronic use of PS-ISO contractions in hamstring strain injury prevention. The potential exists that with the chronic use of PS-ISO contractions, athletes could experience benefits including increased muscle hypertrophy, increased eccentric and isometric strength, increased fascicle length and a rightward shift or broadening of the plateau of the optimum angle in the length-tension curve [12,41,[65][66][67].…”

“…The influence of muscle architecture changes on rFE has recently been investigated, with varied effects found [49,68,69]. For example, Hinks, Davidson, Akagi and Power [67] found no significant changes in rFE following chronic isometric training at long or short muscle lengths, despite the fascicle length increasing and decreasing, respectively [67]. In contrast, evidence of the effect of concentric and eccentric training on rFE is less certain.…”