CrossFit is recognized as one of the fastest growing high-intensity functional training modes in the world. However, scientific data regarding the practice of CrossFit is sparse. Therefore, the objective of this study is to analyze the findings of scientific literature related to CrossFit via systematic review and meta-analysis. Systematic searches of the PubMed, Web of Science, Scopus, Bireme/MedLine, and SciELO online databases were conducted for articles reporting the effects of CrossFit training. The systematic review followed the PRISMA guidelines. The Oxford Levels of Evidence was used for all included articles, and only studies that investigated the effects of CrossFit as a training program were included in the meta-analysis. For the meta-analysis, effect sizes (ESs) with 95% confidence interval (CI) were calculated and heterogeneity was assessed using a random-effects model. Thirty-one articles were included in the systematic review and four were included in the meta-analysis. However, only two studies had a high level of evidence at low risk of bias. Scientific literature related to CrossFit has reported on body composition, psycho-physiological parameters, musculoskeletal injury risk, life and health aspects, and psycho-social behavior. In the meta-analysis, significant results were not found for any variables. The current scientific literature related to CrossFit has few studies with high level of evidence at low risk of bias. However, preliminary data has suggested that CrossFit practice is associated with higher levels of sense of community, satisfaction, and motivation.

This study investigated the effects of a 10-week resistance training to failure on neuromuscular adaptations in young women. Eighty-nine active young women were randomly assigned to one of three groups: 1) repetitions to failure (RF; three sets of repetitions to failure); 2) repetitions not to failure with equalized volume (RNFV; four sets of 7 repetitions); and 3) repetitions not to failure (RNF; three sets of 7 repetitions). All groups performed the elbow flexor exercise (bilateral biceps curl) and trained 2 days per week using 70% of 1RM. There were significant increases (p<0.05) in muscle strength after 5 (15.9% for RF, 18.4% for RNF, and 19.9% for RNFV) and 10 (28.3% for RF, 26.8% for RNF, and 28.3% for RNFV) weeks of training, with no significant differences between groups. Additionally, muscular endurance increased after 5 and 10 weeks, with no differences between groups. However, peak torque (PT) increased significantly at 180°.s-1 in the RNFV (13.7%) and RNF (4.1%) groups (p<0.05), whereas no changes were observed in the RF group (-0.5%). Muscle thickness increased significantly (p<0.05) in the RF and RNFV groups after 5 (RF: 8.4% and RNFV: 2.3%) and 10 weeks of training (RF: 17.5%, and RNFV: 8.5%), whereas no significant changes were observed in the RNF group (3.9 and 2.1% after 5 and 10 weeks, respectively). These data suggest that short-term training of repetitions to failure do not yield additional overall neuromuscular improvements in young women.

The current recommendations on resistance training involving older adults have reported an improvement of body composition variables. Despite this, there is a lack of knowledge on how elastic resistance training (ERT) affects the muscle mass in older adults population. The purpose of this study was to determine the effects of a short-term ERT on muscle mass of health and untrained older adults. Forty older adults were randomized into two groups of 20 individuals each: Control Group (CG = 66.2 ± 6.6 years) and Training Group (TG = 69.1 ± 6.3 years). TG underwent an ERT twice a week during 8 weeks and control group did not receive any specific intervention. The primary outcome was the upper and lower limbs muscle mass, measured by Dual-energy x-ray absorptiometry. The secondary outcomes were knee isokinetic peak torque (PT) at 60°/s and 120°/s speeds and isometric handgrip strength. A 2×2 mixed model (group [TG and CG] × time [pre and post]) analysis of variance (ANOVA) was applied to determine the effect on primary and secondary outcomes. The results of the ANOVA showed no significant effects in group x time interaction for (1) upper limbs fat free mass (F [1.38] = 1.80, p = 0.19, effect size [ES] = 0.1) and for (2) lower limbs fat free mass (F [1.38] = 0.03, p = 0.88, ES = 0.02). Regarding muscle strength, the ANOVA showed no significant effects in group x time interaction for (3) PT at 60°/s (F [1.38] = 0.33, p = 0.56, ES = 3.0), for (4) PT at 120°/s (F [1.38] = 0.80, p = 0.38, ES = 4.1) and for handgrip strength (F [1.38] = 0.65, p = 0.42-value, ES = 0.9). Analysis of PT in TG showed a significant change of 4.5 %, but only at 120°/s (p = 0.01) when comparing pre and post-training (time interaction). Eight weeks of ERT did not show significant changes in muscle mass and strength of untrained older adults. NCT02253615 (09/25/14)

Background: Exercise has been shown to reduce adverse outcomes related to breast cancer. However, the rate of adherence to physical exercise is very low among breast cancer survivors (BCS). This study investigated the effects of high supervision ratio resistance training (RT), once a week for 8 weeks, on changes in body composition and muscular strength in BCS. Methods: Twenty-five female BCS undergoing hormone therapy were randomized into resistance training group (TG, n = 12) or control (CG, n = 13) group. The TG performed 8 weeks of supervised RT, with 1 trainer per volunteer, once a week. Body composition was evaluated by dual-energy X-ray absorptiometry, and muscle strength was evaluated by 10 repetition maximum (10 RM) for leg press (45°) and bench press exercises. A 1-way analysis of variance was used to compare within-group effects at pre- and post-intervention. An analysis of covariance test was used to compare post-intervention values, using pre-intervention measures as covariates. The effect size (ES) was calculated by Cohen’s d. Results: The TG improved muscle strength in 10 RM leg press (45°; Δ 33.75 ± 11.51 kg, P = .02; ES = 0.96) and bench press (Δ 4.08 ± 1.83 kg, P = .01; ES = 1.15). Adherence to training was more than 99%. Changes in body composition were not detected. There were no changes in the CG for any assessment. Conclusion: Once-weekly supervised RT could be an alternative to increase the adherence to exercise and improve muscular strength in BCS.