The influence of training-induced sarcomerogenesis on the history dependence of force

Abstract

The increase or decrease in isometric force following active muscle lengthening or shortening, relative to a reference isometric contraction at the same muscle length and level of activation, are referred to as residual force enhancement (rFE) and residual force depression (rFD), respectively. The purpose of these experiments was to investigate the trainability of rFE and rFD on the basis of serial sarcomere number (SSN) alterations to history-dependent force properties. Maximal rFE/rFD measures from the soleus and extensor digitorum longus (EDL) of rats were compared after 4 weeks of uphill or downhill running with a no-running control. SSN adapted to the training: soleus SSN was greater with downhill compared with uphill running, while EDL demonstrated a trend towards more SSN for downhill compared with no running. In contrast, rFE and rFD did not differ across training groups for either muscle. As such, it appears that training-induced SSN adaptations do not modify rFE or rFD at the whole-muscle level.

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

“…Hence, the fascicle length adaptations we observed did not appear to impact voluntary rFE. This agrees with the findings of Power et al, 46 in which agerelated decreases in fascicle length did not contribute to differences in rFE, and Chen et al, 43 in which changes to serial sarcomere number did not impact absolute and relative rFE. Chen and Power, 17 however, saw an 89% increase in relative rFE following concentric training and a 36% decrease following eccentric training that corresponded to changes in fascicle length.…”

“…Fascicle length changed as expected following short-and long-MTU training ( Figure 4) and those changes did not relate to changes in relative rFD ( Figure 5A), therefore, the passive fascicle length adaptations we observed did not appear to impact voluntary rFD. These results echo those found by Chen and Power,17 in which relative rFD did not change following concentric or eccentric training, as well as those from Chen et al, 43 in which serial sarcomere number changes in rats following uphill and downhill running training did not alter absolute and relative rFD in vitro.…”

“…Based on animal studies, we can speculate that these adaptations come from decreases (short-MTU training) and increases (long-MTU training) in serial sarcomere number to reduce compression or stretching of existing sarcomere overlap regions for more optimal cross-bridge formation, and consequently force production. 21,22,43…”

“…Previous studies saw no change to work during active shortening and no change to the corresponding rFD following eccentric and concentric training, 17 nor uphill and downhill running training. 43 This adaptation specific to isometric dorsiflexion training may have application in optimizing performance, allowing the muscle to perform more work during a concentric contraction without incurring additional rFD.…”

The Time-Course of Changes in Muscle Mass, Architecture and Power During 6 Weeks of Plyometric Training

“…Similarly to Blazevich et al (2003), our results show increases in VL Lf following PLT; this phenomenon is expected to reflect an increase in the number of sarcomeres in series, and thus in maximum shortening velocity (Bodine et al, 1982). Animal studies have shown that sarcomere addition can occur already after 5, 10, and 28 days in response to training modalities involving muscle lengthening (Lynn et al, 1998;Butterfield et al, 2005;Chen et al, 2020). However, recent studies in intact whole mice muscle have described some variability in sarcomere length along different muscle regions (Moo et al, 2016), which become even more non-uniform upon activation (Moo et al, 2017).…”