Acute Metabolic and Muscle Oxygenation Responses to Different Eccentric Tempos Under a Fixed Velocity-Loss Threshold in Squat

Purpose: This study explored the acute physiological effects of different eccentric tempos, explosive speed (EXP), volitional speed, and 4-second tempo during 5 sets of velocity-based squat training. Methods: Twelve healthy males performed parallel squats under 3 eccentric conditions using a randomized crossover design. Each session included 5 sets at a relative load, initiated with a concentric mean velocity of 0.70 m·s⁻¹, continuing until 20% velocity loss, with 300-second rest intervals. Blood lactate concentration was measured preexercise and postexercise each set, while changes in muscle tissue saturation index, deoxygenated hemoglobin, oxygenated hemoglobin, and total hemoglobin were continuously monitored during training using near-infrared spectroscopy. Results: The 4-second eccentric tempo resulted in significantly greater increase in lactate than EXP (3.82 [1.0] vs 2.89 [0.8] mmol·L⁻¹, P = .002) and a higher area under the curve of lactate (4 s: 112.9 [22.8] vs EXP: 93.8 [25.1] mmol·L⁻¹·min, P = .003, d = 1.02). Changes in tissue saturation index, deoxygenated hemoglobin, and oxygenated hemoglobin and time under tension were significantly higher in the 4-second trial than in the EXP and volitional speed trials (P < .05). No significant differences were observed in the changes in total hemoglobin, number of repetitions, training volume, mean velocity, mean power, or subjective perceptions (P > .05). Conclusions: A 4-second eccentric tempo induces greater metabolic and oxygenation responses under identical velocity-loss conditions while preserving power output and subjective perceptions. These findings highlight eccentric velocity as a key variable in velocity-based training, particularly for optimizing metabolic stress and training adaptations.