Multivariate analysis in the maximum strength performance

This study performed an exploratory analysis of the anthropometrical and morphological muscle variables related to the one-repetition maximum (1RM) performance. In addition, the capacity of these variables to predict the force production was analyzed. 50 active males were submitted to the experimental procedures: vastus lateralis muscle biopsy, quadriceps magnetic resonance imaging, body mass assessment and 1RM test in the leg-press exercise. K-means cluster analysis was performed after obtaining the body mass, sum of the left and right quadriceps muscle cross-sectional area (Sigma CSA), percentage of the type II fibers and the 1RM performance. The number of clusters was defined a priori and then were labeled as high strength performance (HSP1RM) group and low strength performance (LSP1RM) group. Stepwise multiple regressions were performed by means of body mass, Sigma CSA, percentage of the type II fibers and clusters as predictors' variables and 1RM performance as response variable. The clusters mean +/- SD were: 292.8 +/- 52.1 kg, 84.7 +/- 17.9 kg, 19249.7 +/- 1645.5 mm(2) and 50.8 +/- 7.2% for the HSP1RM and 254.0 +/- 51.1 kg, 69.2 +/- 8.1 kg, 15483.1 +/- 1 104.8 mm(2) and 51.7 +/- 6.2 %, for the LSP1RM in the 1RM, body mass, Sigma CSA and muscle fiber type II percentage, respectively. The most important variable in the clusters division was the Sigma CSA. In addition, the Sigma CSA and muscle fiber type II percentage explained the variance in the 1RM performance (Adj R-2 = 0.35, p = 0.0001) for all participants and for the LSP1RM (Adj R-2 = 0.25, p = 0.002). For the HSP1RM, only the Sigma CSA was entered in the model and showed the highest capacity to explain the variance in the 1RM performance (Adj R-2 = 0.38, p = 0.01). As a conclusion, the muscle CSA was the most relevant variable to predict force production in individuals with no strength training background.

Injuries in strength training: review and practical application

Purpose: This systematic review examines what is known about injuries in strength training. Methods: A systematic search was performed in PubMed and SportDiscus. Studies were included if they examined powerlifters, weightlifters, strongman athletes, bodybuilding athletes, individuals who undertook recreational weight training or weight training to complement athletic performance. Exposure variables were incidence, severity and body part injury. Results: After examining 1214 titles and abstracts, 62 articles were identified as potentially relevant. Finally, 11 were included in this systematic review. Conflicting results were reported on the relationships between injury definition and incidence or severity recorded. The lower back followed by the shoulder and knee are the most frequently affected areas in strength sports. Conclusion: Strength training is safe. However, the variety of injury definitions has makes it difficult to compare different studies in this field. New styles of reporting injuries have appeared, and could make increases these ratios. If methodological limitations in measuring incidence rate and severity injuries can be resolved, more work can be conducted to define the real incidence rate, compare it with others sports, and explore cause and effect relationships in randomized controlled trials. Key Words: strength training, injuries, specific strength sports, severity