Loaded inter-set stretch may selectively enhance muscular adaptations of the plantar flexors

Abstract

The purpose of this study was to evaluate differences in changes in muscle strength and muscle thickness (MT) of the plantar flexor muscles between traditional resistance training (RT) involving passive rest and RT combined with inter-set stretch in the calf raise exercise. Employing a within-subject design, 21 young, healthy men performed plantar flexion exercises twice per week in both a traditional RT (TRAD) format and combined with a 20-second inter-set stretch (STRETCH). One leg was randomly assigned to the TRAD condition and the contralateral leg performed the STRETCH condition throughout the 8-week study period. Dependent variables included MT of the lateral gastrocnemius (LG), medial gastrocnemius (MG) and the soleus (SOL), and isometric strength of the plantar flexors. Results indicated a potential beneficial hypertrophic effect of STRETCH compared to TRAD for the SOL [0.7 mm, CI90% = (0, 1.6)], while the LG had more ambiguous effects [0.4 mm (−0.4, 1.3)] and MG effects were equivocal [0 mm (−0.6, 0.7)]. In general, LG demonstrated greater standardized growth [z = 1.1 (1, 1.3)] as compared to MG [z = 0.3 (0.2, 0.5)] and SOL [z = 0.3 (0.2, 0.5)]. Measures of isometric strength showed a modest advantage to STRETCH. In conclusion, loaded inter-set stretch may enhance MT of the soleus but effects on the gastrocnemii appear uncertain or unlikely in untrained men; plantar flexor strength appears to be modestly enhanced by the interventional strategy.

Inter-set stretch: A potential time-efficient strategy for enhancing skeletal muscle adaptations

“…However, given that several studies have observed beneficial hypertrophic effects with no evidence of a detriment, the strategy would seem to have a good cost-benefit profile. Intriguingly, despite some research showing acute strength impairments subsequent to static stretching protocols ( 64 ), current research does not indicate deleterious effects across different populations on long-term strength outcomes and in some instances the strategy shows positive adaptations ( 59 , 62 ).…”

“…As noted, avian models of loaded stretch show greater hypertrophy in muscles comprised predominantly of type I compared to type II myofibers ( 46 ). The aforementioned study by Van Every et al ( 59 ) found that inter-set stretch elicited greater hypertrophy in the soleus, a type I dominant muscle, compared to the gastrocnemii, a mixed-fiber muscle. Replication of these findings and further research into the mechanisms of inter-set stretch is needed to better understand this phenomenon and its potential practical implications to program design.…”

“…In a within-subject design, Van Every et al ( 59 ) randomized the lower limbs of untrained young men to perform plantar flexion exercises with either a 2-min passive rest period or a 20-s inter-set stretch at the same working load followed by 100 s of passive rest. After 8-weeks, results showed greater increases in muscle thickness of the soleus for the stretch condition compared to control; these results were observed despite a decrease in RT volume load (5 to 12%) in the stretch condition.…”

“…Results showed that improvements in strength measures tended to favor stretch compared to control; however, increases in quadriceps muscle thickness were generally similar between conditions. It should be noted that the stretch condition in this study involved moving from the flywheel unit to a massage table and then assuming the designated stretch ( 62 ), whereas the aforementioned studies performed inter-set stretch immediately after each set of RT ( 57 – 59 ). This time lag from moving between the exercise to the table and getting properly positioned for the stretch may have diminished the residual effects of eccentric actions on the ensuing stretch, and thus impaired hypertrophic enhancements.…”

Triceps surae muscle hypertrophy is greater after standing versus seated calf-raise training

“…Based on these, triceps surae muscle hypertrophy may be greater after standing than seated calf-raise training. Both standing and seated calf-raise are common exercises to train the triceps surae, and have been often implemented alone ( Carson et al, 2010 ; Gavanda et al, 2020 ; Kudo et al, 2020 ) or in combination ( Schoenfeld et al, 2020 ; Kataoka et al, 2022 ; Van Every et al, 2022 ) in previous studies. However, no study has compared their hypertrophic effects through training interventions.…”