Performance of unstable barbell bench press and changes in electromyographic activity after transcranial direct current stimulation

Abstract

BACKGROUND: Transcranial direct current stimulation can enhance human motor performance by modulating cortical excitability, but its impact on the performance of unstable resistance exercise remains unclear. OBJECTIVE: To investigate the effects of transcranial direct current stimulation on unstable barbell bench press performance and electromyographic activity. METHODS: A randomized, self-controlled crossover design was employed. Twenty-two male college students were randomly assigned to receive either active anodal transcranial direct current stimulation or sham stimulation. After transcranial direct current stimulation interventions, subjects performed a fatigue test involving the unstable barbell bench press. Performance during the unstable barbell bench press task was assessed by recording both the number of completed repetitions and barbell acceleration, serving as indicators of load capacity and movement stability control. In addition, surface electromyographic signals were collected from the right biceps brachii, triceps brachii, anterior deltoid, posterior deltoid, and pectoralis major during the exercise. A paired t-test was used to examine differences in repetition counts between true and sham stimulation conditions. Repeated measures analysis of variance was applied to analyze differences in triaxial acceleration, agonist muscle activation levels, and antagonist co-activation levels. RESULTS AND CONCLUSION: (1) No significant difference in the number of barbell bench press repetitions was observed between the true and sham stimulation conditions. However, the mean amplitude of Y-axis acceleration was substantially lower in the true stimulation group than the sham stimulation group. (2) True transcranial direct current stimulation markedly increased the activation level of the anterior deltoid and the co-activation level of the posterior deltoid. (3) There was no significant interaction between transcranial direct current stimulation and exercise phase on any measured variable. (4) These findings suggest that transcranial direct current stimulation does not significantly affect muscle endurance performance during unstable barbell bench press, but it can improve movement stability, possibly by increasing anterior deltoid activation and posterior deltoid co-activation, thereby enhancing shoulder joint stiffness and stability. In competitive sports and clinical rehabilitation, transcranial direct current stimulation may be considered to modulate performance in unstable load-bearing tasks according to training objectives.

1. Introduction

With the rapid development of neuroscience and in-depth research on the brain and nervous system, non-invasive neuromodulation techniques are gradually becoming novel means to enhance human motor performance and address health issues. Transcranial direct current stimulation (tDCS), as an economical and convenient non-invasive neuromodulation technique, has gained widespread attention in recent years. Previous studies have shown that tDCS can modulate the excitability of the motor cortex, improve regional cerebral blood flow, enhance synaptic plasticity and brain network connectivity, and improve neuromuscular control [1-2]. Studies have found that tDCS can effectively increase muscle strength [3], delay muscle fatigue [4], improve balance control, and enhance motor skill learning efficiency [5-6]. However, some studies have reported no improvements in muscle strength, endurance, or balance control following tDCS [7]. Therefore, the effectiveness of tDCS in enhancing human motor performance remains controversial, possibly due to factors such as stimulation parameters and task specificity.

Unstable load-bearing exercise is a form of resistance training performed under unstable conditions. It is common in competitive sports and daily activities, and serves as an important training and rehabilitation modality [8]. During such tasks, individuals must coordinate limb stability while overcoming external loads, increasing task difficulty and imposing greater demands on the neuromuscular system [9]. Previous research has demonstrated that appropriate unstable load training can yield superior outcomes in muscle strength, endurance, and balance compared to traditional resistance training [10]. The barbell bench press is a common upper-limb strength test and training exercise, and when performed on an unstable surface, it challenges both force production and postural control.