Task‐specific strength increases after lower‐limb compound resistance training occurred in the absence of corticospinal changes in vastus lateralis

Abstract

Neural adaptations subserving strength increases have been shown to be task-specific, but responses and adaptation to lower-limb compound exercises such as the squat are commonly assessed in a single-limb isometric task. This two-part study assessed neuromuscular responses to an acute bout (Study A) and 4 weeks (Study B) of squat resistance training at 80% of one-repetition-maximum, with measures taken during a task-specific isometric squat (IS) and non-specific isometric knee extension (KE). Eighteen healthy volunteers (25 ± 5 years) were randomised into either a training (n = 10) or a control (n = 8) group. Neural responses were evoked at the intracortical, corticospinal and spinal levels, and muscle thickness was assessed using ultrasound. The results of Study A showed that the acute bout of squat resistance training decreased maximum voluntary contraction (MVC) for up to 45 min post-exercise (−23%, P < 0.001). From 15-45 min post-exercise, spinally evoked responses were increased in both tasks (P = 0.008); however, no other evoked responses were affected (P ≥ 0.240). Study B demonstrated that following short-term resistance training, participants improved their one repetition maximum squat (+35%, P < 0.001), which was reflected by a task-specific increase in IS MVC (+49%, P = 0.001), but not KE (+1%, P = 0.882). However, no training-induced changes were observed in muscle thickness (P = 0.468) or any evoked responses (P = 0.141). Adjustments in spinal motoneuronal excitability are evident after acute resistance training. After a period of short-term training, there were no changes in the responses to central nervous system stimulation, which suggests that alterations in corticospinal properties of the vastus lateralis might not contribute to increases in strength.

Training load but not fatigue affects cross‐education of maximal voluntary force

“…Meta-analytic evidence suggests that RT increase CSE in the trained limb when measured during contraction, 36 but do not change in the untrained limb. 10 However, our results do not support the role of an increased CSE as a mechanism to improve force in either leg, which agrees with previous studies that also found no changes 17,18,37 or even decreases 38 in CSE when measured at rest and during contraction in the trained limb, or no changes at rest or during contraction in the untrained limb. 10 Reductions in CSE in the trained muscles after a short-term RT have been suggested to be related to an increase in corticospinal efficiency that reduces the neural resources needed to perform the task during which measurements are obtained.…”

“…9 However, the lack of correlation between changes in maximal force and CSE of the corresponding limb (either trained or untrained) agrees with previous reports of the absence of correlation between CSE and performance in ballistic contractions 40 and casts doubts about the role of CSE as a mechanism contributing to force increases. It is possible that force increases may be related to adaptations in other descending tracts with a role in force generation, 37 like the reticulospinal tract, 41,42 which could not be detected by TMS of the motor cortex, or in motor cortex structures involved in other TMS outcomes not tested in the present study (ie, changes in intracortical circuits). 17,36 The present study has some limitations that could have influenced the results or limited the conclusions.…”

Flywheel squats versus free weight high load squats for improving high velocity movements in football. A randomized controlled trial

“…A meta-analysis reported that FW RE is not superior to traditional RE for strength improvements [45], which corroborate our findings. Nevertheless, the difference in 1RM squat strength between the BFW and the FW group in our study is likely an effect of test specificity where the exercise performed by the BFW group was isotonic to the test; this is shown previously for the squat exercise [46]. Consequently, we urge for cautious interpretation when comparing 1RM gains between the BFW and FW group.…”

Neural adaptations to long-term resistance training: evidence for the confounding effect of muscle size on the interpretation of surface electromyography

“…However, M max has also been shown to remain unchanged following short-term resistance training (≤7 weeks; Refs. 3,17,21,51), despite a study of similar duration showing increases in conduction velocity (12), suggesting that increased conduction velocity of motor units might not necessarily be related to increased M max amplitude in the context of resistance training.…”