“What trains together, gains together”: strength training strengthens not only muscles but also neural networks

Abstract

"WHAT FIRES TOGETHER, WIRES TOGETHER" (8): on the cellular level, the use-dependent plasticity of neural networks has been known for over 60 years. Dependent on the timing of pre-and postsynaptic activation, transmission across synapses can either be facilitated or inhibited (2). On the level of the whole organism, these neural adaptations are thought to be the first step in a series of others to improve specific motor skills. Thus, depending on the learning stage, motor skill acquisition involves different physiological processes. In the human motor cortex, for instance, long-term potentiation (LTP) is thought to occur at existing synapses during the early phase of motor skill learning, whereas later phases involve neural processes like synaptogenesis (10).Similar to motor skill learning, strength training comprises different stages, which differ with respect to the substrate of adaptation. The early force gains after strength training are thought to rely primarily on neural adaptations, while later on, structural changes within the tendomuscular system are considered to be predominant. So far, it is unknown whether the early neural plasticity after strength training relies on similar mechanisms than the one after motor skill training. Although previous electrophysiological strength training studies could indeed demonstrate that neural adaptations take place at the spinal and supraspinal level, the findings of those reports are inconsistent (for review, see 5): some studies assumed increased spinal excitability (e.g., 1, 13) while results obtained in other experiments suggested the opposite (e.g., 4). Similarly, some authors reported enhanced corticospinal excitability following strength training (7) whereas others did not (4, 9). These discrepancies may be due to a differential contribution of the central nervous system (CNS) in different strength tasks (static vs. dynamic, tonic vs. ballistic, etc.), may depend on the duration of the training intervention, and/or may be related to methodological reasons. In this respect it could be demonstrated that adaptations assessed at rest may differ from adaptations measured during activity (e.g., 1, 9). Furthermore, when subjects were tested during a task they had previously trained, changes of the corticospinal excitability were opposed to those observed after measurements in an unfamiliar task involving the same muscles (11).The above-mentioned examples highlight that there is the need for further research and especially new methodological approaches in order to gain a better understanding of the mechanisms related to strength training. In this issue of the Journal of Applied Physiology, Selvanayagam and colleagues (12) provide such a new insight in their paper "Early neural responses to strength training" as they have chosen an experimental set-up in which the neural plasticity in response to one single session of strength training, could be directly observed in changes of the behavioral outcome. The experiment was designed based on a previous motor control study of...

Strength Training Biases Goal-Directed Aiming

“…The authors highlighted that increased responses to brain stimulation were likely to be dominated by spinal level factors, although precise contributions were difficult to assess because a direct In our previous study, we proposed that strengthening of connections within neural networks in favour of the training direction occurs early in strength training (30,36). Here we extend knowledge of the acute responses to strength training to show that such effects can affect voluntary aiming behavior.…”

“…Evidence for such changes can be observed after a single session of isometric strength training, via changes in the direction of muscle twitched evoked by transcranial magnetic stimulation (TMS;30). This implies that strength training can alter neural connectivity within the human primary motor cortex or its downstream projections (30,36). These findings are similar to those observed in response to extensive practice of simple ballistic finger tasks (4,8), suggesting that responses to strength training may be brought about by a form of "use-dependent learning".…”

Strength training reduces intracortical inhibition

“…, Carroll et al . , Taube ). In this study, the reduction in SICI indicates a lesser amplitude of IPSPs.…”

Strength Training with Superimposed Whole Body Vibration Does Not Preferentially Modulate Cortical Plasticity

“…Skill training is defined as the acquisition and subsequent refinement of novel combinations of movement sequences [32]. Based on this rationale, it has been suggested that some strength training programs may be considered a form of skill training [11, 33]. In the present study, all participants were untrained and performed unfamiliar multijoint strength training with explicitly controlled repetition timing and depth.…”