Effects of resistance training modality on physical performance and muscle structure

Zusammenfassung

Throughout a rigorous evaluation and programming methodology, the main objective of this Doctoral Thesis was to compare the effects of free-weight and machine-based resistance training on physical performance and muscle structure. This methodology was thoroughly examined in Studies I and II (Articles 1-5) and subsequently implemented in the Articles developed to address the main research question underlying this project (Study III, Articles 6 and 7). Article 1 aimed to analyze the load-velocity (L-V) relationship of the free-weight and machine-based modalities of squat (SQ), bench press (BP), prone bench pull (PBP) and shoulder press (SP) exercises, as well as to examine the influence of the subject's strength level on these L-V relationships. Analyses showed very close adjustments (R2 0.95) for the 8 L-V relationships examined, which exhibited not being conditioned by the subject's strength level but by the training modality (velocity attained at each intensity was significantly faster for the free-weight variant). Article 2 examined the suitability of the level of effort method to program the intensity and intraset volume in SQ, BP, PBP, and SP exercises. Regardless of the subject's strength level, this study found very low inter- (Confidence interval, CI 95% 4 repetitions) and intra-subject (Standard error of the measurement, SEM 2 repetitions) variability in nRM, as well as a high relationship (R2 0.97) between the repetitions completed and velocity loss incurred. Articles 3 and 4 quantified acquisition and analysis errors made when implementing ultrasound to assess the anatomical cross-sectional area (ACSA) of the pectoralis major (Article 3) and quadriceps (Article 4). Acquisition errors included the comparison of two images acquired 5 min apart, while the first acquisition was analyzed twice to quantify analysis errors. Moreover, the ACSA from the first acquisition was compared with that obtained by magnetic resonance imaging (MRI). These errors were quantified for a trained and a novice sonographer. Both Articles revealed small errors (especially for the trained sonographer) when acquiring and analyzing ACSA of these muscles, as well as high agreement with MRI. On the other hand, Article 5 examined the agreement between quadriceps ACSA (considering all the muscles together) measured by ultrasound and MRI, as well as the validity and reliability of two approaches of the 2-point method (using the 30-60% or 20-70% thigh regions) for estimating ultrasound-derived quadriceps femoris ACSA. Besides almost perfect agreement (r 0.968) between ultrasound and MRI, this study found small estimation and test-retest errors for the 2-point20-70% (SEM 5.67 cm2) but especially for the 2-point30-60% (SEM 3.62 cm2). All these results laid the methodological basis for Study III. Articles 6 and 7 compared the effects of free-weight and machine-based resistance training on physical performance, muscle structure, and discomfort levels. For this purpose, 34 (Article 6) and 38 (Article 7) males completed an 8-week velocity-controlled training allocated into free-weight or machine-based groups. All training parameters were identical for both modalities, so they only differed in the use of barbells or machines for performing SQ, BP, PBP, and SP exercises. Changes in physical performance were compared in 5 athletic (sprint, change of direction, vertical jump, balance, upper- and lower-limb anaerobic cycling performance) and 8 strength tests. The ACSA of the quadriceps, pectoralis major and rectus abdominis, as well as the muscle architecture of the vastus lateralis, were measured to examine structural changes. Furthermore, the DASH and WOMAC questionnaires were administered to assess changes in upper- and lower-limb discomfort, respectively. Results of both studies suggest that free-weight and machine-based training modalities would be similarly effective to promote physical performance and structural changes without increasing joint discomfort.