D. Kaczynski, A. Barnett, J. Turner, A. Harkins, D.B. Thorp

Gonzaga University, Spokane, WA

PURPOSE: The purpose of this study was to determine if deceptive placebo supplementation increases force production during an isometric mid-thigh pull (IMTP). It was hypothesized that acute ingestion of a placebo supplement (cornstarch) would lead to increased force during the IMTP, and force production to be further increased following daily supplementation for one week. It was also hypothesized these effects would be more pronounced in habitual supplement users. METHODS: 13 weightlifters (10 male, 3 female, age: 20.4 ± 0.8 years) participated. Following a warm-up, subjects performed three six-second IMTPs on a force plate, followed by a cool-down. Subjects assumed a deadlift position with shoulders over knees over hips, and knee angle between 120-140 degrees. Subjects were tested on four occasions: familiarization, baseline (BL), acute supplementation (AS - two supplements taken 20 minutes prior to warm-up), and loaded supplementation (LS - one supplement taken in morning and one in evening daily for seven days). Force was collected at 100Hz. Peak force (PF), average force (AF), explosiveness (EXP) and fatigue index (FI) were calculated for each IMTP, and the three trials averaged for each condition. A mixed model repeated measures ANOVA compared IMTP performance between conditions, and between habitual supplement users and non-supplement users. Data was analyzed with IBM SPSS Version 23.0, p<0.05. RESULTS: LS resulted in lower FI (9.92 ± 4.03%) from to BL (14.98 ± 4.75%, p=0.002) and AS (17.20 ± 8.45%, p=0.001). FI was not affected by AS compared to BL (p=0.355). LS resulted in increased AF (2006.53 ± 396.80N) from BL (1946.73 ± 424.54N, p=0.019), yet was not different from BL to AS (1970.35 ± 423.36N, p=0.057), or from AS to LS (p=0.085). PF (p=0.469) and EXP (p=0.545) were not different between BL, AS and LS. Habitual supplement users had greater PF (p=0.046) and AF (p=0.030) than non-supplement users, yet differences between groups among supplement conditions were not significant. CONCLUSION: This study supports deceptive placebo supplementation is effective in improving performance of isometric exercise due to expectancy theory. Placebo supplementation may have influenced subjects to maintain force and delay fatigue, only after loaded placebo supplementation.

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