A. Guevara, A. Morse, C. Murbach, S. Ross, R. Stanley, J. McKenzie

Gonzaga University, Spokane, WA

Postactivation potentiation (PAP) is a neuromuscular mechanism that increases the force of a muscle due to previous contractions through MLCK phosphorylation, promoting stronger contraction in a shorter duration and increased excitability. The effects of PAP on exercises involving a mix of type I and type II muscle fibers, have not been studied extensively. PURPOSE: This study examined the potential PAP inducing effect of an acute isometric muscle contraction, on subsequent 1,000m rowing sprint performances. METHODS: 19 trained collegiate rowers performed two 1,000m sprints using a repeated-measure, counterbalanced design over a 4 week period. The control group (CO) had a warm-up row, followed by a 7-minute rest period preceding the 1,000m sprint. The intervention group (WS) performed a warm-up row along with a wall-sit exercise, followed by a 7-minute rest period and the 1,000m sprint. Warm-up duration was controlled for between trails. Time to completion (TTC), power output, and stroke rating was collected following each sprint. Heart rate (HR) and rate of perceived exertion (RPE) was collected periodically throughout the study. Blood lactate concentration was measured immediately following the 1,000m sprints. All measured variables were compared between CO and WS trials using a dependent paired t-test. RESULTS: There were no significant differences in TTC (mean diff = -.3 s, p=.764) and average power (mean diff = .0 W, p=.990) between conditions. RPE values were significantly higher following the WS warm up protocol (mean diff = -3, p<.001), as well as post rest period in the WS trials (mean diff = -2, p=.004). A significant positive correlation was found between RPE after the warm up during the intervention (RPEWI) and power (r = .479, p = .038) and a significant negative correlation between RPEWI and time (r = -.493, p = .032). CONCLUSION: The correlation between RPEWI values and TTC suggests that PAP may have been elicited. However, since TTC values were not significantly different between trials, the PAP effect was potentially blunted by factors such as muscle fiber type recruited, the primarily aerobic exercise, and subjects’ body composition. For a significant PAP effect to be produced, type II muscle fibers must be recruited, the exercise must be anaerobic, and subjects’ must have high amounts of fat free mass.

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