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In this study, we investigated the influence of isothermal treatment of poly(lactic acid) (PLA) 3D printed samples at different crystallization temperatures. In this case, we analyzed the effect of each crystallization temperature on spherulites formation in printed PLA, affecting the final mechanical properties of pieces. For such, the thermomechanical properties, morphological structure, and crystallization kinetics were analyzed before and after thermal treatment. The 3D printed samples were heat treated at 80°C, 90°C, 100°C, 110°C, and 119°C. With annealing, we observed an improvement in the mechanical PLA properties; however, the exothermic crystallization peak was different for the samples. Pieces before annealing were found to have a low crystallinity index (Ic) of 2%–7%, and the pieces after annealing presented a considerable Ic (27%–34%). Annealing temperatures of 100°C, 110°C, and 119°C produced the fastest crystallization kinetics, while annealing temperatures of 80°C and 90°C resulted in the lowest crystallization kinetics for complete crystallization. After annealing, improvement in the flexural strength (34%–47%) and Young's modulus (26%–51%) for all annealed pieces occurred. The appropriate condition was observed at 100°C, which was the onset temperature of crystallization, owing to the combination of the shorter time of crystallization with the increased mechanical properties.

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Purpose. The objective of the study was to assess the effects of a 4-week intensified period of in-season soccer training with addition of explosive training and beta-hydroxy-beta-methylbutyrate (HMB) supplementation on maximal-intensity and endurance performance in young male soccer players, compared with a parallel training with placebo (i.e. magnesium stearate) supplementation. Methods. A randomized, double-blind, placebo-controlled trial was conducted. Male athletes (age, 18.6 ± 1.4 years) were assigned either to a group receiving HMB supplementation (n = 9) or to a placebo group (n = 7). Results. The athletes were evaluated for maximal-intensity jumping and endurance performance before and after the intervention. Before the intervention, the two groups were characterized by similar age, body mass, height, and soccer experience. In addition, no differences between groups were observed for physical performance measures other than a greater countermovement jump performance in the HMB group compared with the placebo group. After the intervention, neither group showed any significant change in any of the physical performance measures. Conclusions. Compared with a 4-week intensified period of in-season soccer training with addition of explosive training and placebo supplementation, HMB supplementation did not add further adaptive changes related to maximal-intensity and endurance performance in young male soccer players.