THE INFLUENCE OF LIFTING STRAPS ON ISOMETRIC BACK EXTENSOR MUSCLE STRENGTH MECHANICAL CARACTHERISTICS: A STUDY OF POWERLIFTERS

The aim of this study was to investigate how lifting straps affect isometric back extensors muscle strength. The participants were divided according to gender and training level: trained – powerlifters (n = 17) and control – a specifically non-trained group (n = 24). For the purposes of this study, the maximum voluntary contraction of the back extensors was measured in isometric conditions in the isometric back extension exercise. After a 5-minute standard and specific warm-up, the participants had three trials each with lifting straps and without lifting straps, with a break of 2 minutes between trials. They were given the verbal instruction "pull as hard and fast as possible” and hold for 2 to 3 seconds. Repeated measures ANOVA showed a general statistically significant difference (p<0.05) between testing procedures (classical and straps). A paired samples t-test was used to determine differences between maximal and explosive strength variables. Then, the percentage difference (Δ) of all variables (Fmax - maximal force, RFDmax - maximal rate of force development, tFmax - time needed to reach maximal force, tRFDmax - time for maximal rate of force development) was calculated using the formula: Fmax_Δ = ((Fmax_straps - Fmax_class) / Fmax_class) *100. Differences in the maximum isometric back extension force (Fmax) were found in both groups (powerlifter males - p = 0.004, females - p = 0.019 and control group males - p = 0.018, females – p = 0.001), while differences in tFmax were observed only in the control group (males – p = 0.001 and females - p = 0.000). The results showed that lifting straps have a positive effect in measuring supra-maximal isometric strength (averaged enhancement was 15.93±4.58% regardless of gender and training status), and can potentially be used in a methodological sense to determine the objective values of the biological contractile potential in terms of maximum strength, in pulling type of exercises that include a hand grip (the deadlift, lat pull down, mid-thigh pull test).