The impact of observing dynamic vs. isometric fatiguing contractions on subsequent strength performance

Action observation (AO) and empathy engage neural networks involved in motor execution, suggesting that watching others perform actions might influence one's own motor behavior. It remains unclear whether observing fatigue-inducing contractions, affects subsequent performance. Sixteen recreationally active participants completed maximal voluntary isometric contractions and dynamic tasks under both observation and no-observation conditions in a randomized, cross-over design. Key outcomes including quadriceps and hamstrings electromyography (EMG), maximal voluntary isometric contraction (MVIC) force, repetition count, heart rate, and ratings of perceived exertion (RPE). Repeated measures ANOVAs revealed significant and near significant main effects of time for quadriceps EMG F(5,75) = 14.9, (p < 0.001), hamstrings EMG (F(5,75) = 2.08, p = 0.07), and MVIC (F(1.42, 19.68) = 14.04, p < .001. As expected, fatigue-related decreases in force and EMG activity were observed over time, indicating typical fatigue progression. However, no differences emerged between the observation and control conditions for any variables, suggesting that watching a confederate perform fatiguing actions does not alter motor performance, neuromuscular activation, or subjective effort. These findings highlight that visual exposure to fatigue in others is insufficient to modulate subsequent motor or perceptual responses. This underscores the importance of incorporating emotional salience, social relevance, and task engagement, when aiming to apply them effectively in sports and rehabilitation settings.