Effect of exercise training on insulin-stimulated glucose disposal: a systematic review and meta-analysis of randomized controlled trials.

BACKGROUND AND OBJECTIVE: The effect of exercise training on whole-body insulin sensitivity has not been systematically summarized. We aimed to summarize the data from randomized controlled trials evaluating the effect of exercise training on insulin action, in adults. SUBJECTS: MEDLINE, EMBASE, and CENTRAL databases were searched until January 2021. Randomized controlled trials lasting ≥4 weeks, including adults, and evaluating the effect of exercise on insulin-stimulated glucose disposal measured using the hyperinsulinemic euglycemic clamp, were included. METHODS: Three reviewers extracted summary data from published trials. The primary outcome was insulin-stimulated glucose disposal. Standardized weighted mean differences (SMD) in glucose disposal between intervention and control were compared. The PEDro scale was used to assess risk of bias. RESULTS: We included 25 trials (36 interventions, N = 851). Exercise increased insulin-stimulated glucose disposal relative to control, SMD = 0.52 (95% confidence interval [CI]: 0.39, 0.65; p < 0.001; I2 = 47%) without significantly suppressing hepatic glucose production. In trials without isotopic tracers, exercise increased glucose disposal (SMD = 0.63; 95% CI: 0.48, 0.77; p < 0.001, I2 = 55%). In trials with isotopic tracers, exercise increased glucose disposal only when tracers were added to the exogenous glucose used for clamping (SMD = 0.34; 95% CI: 0.03, 0.66, p = 0.034. I2 = 0%). In a meta-regression model including aerobic exercise, weight change, and tracer technique, only percent weight change explained between trial heterogeneity (ß = 0.069; 95% CI: 0.005, 0.013). The PEDro rating indicated relatively low risk of bias (5.8 ± 0.22). CONCLUSIONS: Exercise training for at least four weeks significantly increases insulin-stimulated glucose disposal. Weight loss maximizes the effect and may be needed to improve hepatic insulin sensitivity. Differences in tracer methodology contribute to divergent outcomes and should be considered when assessing conclusions from research examining the effect of exercise on insulin action. REGISTRATION: PROSPERO (CRD42019124381).

Effects of Field Position on Fluid Balance and Electrolyte Losses in Collegiate Women's Soccer Players.

Research investigating hydration strategies specialized for women's soccer players is limited, despite the growth in the sport. The purpose of this study was to determine the effects of fluid balance and electrolyte losses in collegiate women's soccer players. Eighteen NCAA Division I women's soccer players were recruited (age: 19.2 ± 1.0 yr; weight: 68.5 ± 9.0 kg, and height: 168.4 ± 6.7 cm; mean ± SD), including: 3 forwards (FW), 7 mid-fielders (MD), 5 defenders (DF), and 3 goalkeepers (GK). Players practiced outdoor during spring off-season training camp for a total 14 practices (WBGT: 18.3 ± 3.1 °C). The main outcome measures included body mass change (BMC), sweat rate, urine and sweat electrolyte concentrations, and fluid intake. Results were analyzed for comparison between low (LOW; 16.2 ± 2.6° C, n = 7) and moderate risk environments for hyperthermia (MOD; 20.5 ± 1.5 °C, n = 7) as well as by field position. The majority (54%) of players were in a hypohydrated state prior to practice. Overall, 26.7% of players had a %BMC greater than 0%, 71.4% of players had a %BMC less than -2%, and 1.9% of players had a %BMC greater than -2% (all MD position). Mean %BMC and sweat rate in all environmental conditions were -0.4 ± 0.4 kg (-0.5 ± 0.6% body mass) and 1.03 ± 0.21 mg·cm-2·min-1, respectively. In the MOD environment, players exhibited a greater sweat rate (1.07 ± 0.22 mg·cm-2·min-1) compared to LOW (0.99 ± 0.22 mg·cm-2·min-1; p = 0.02). By position, DF had a greater total fluid intake and a lower %BMC compared to FW, MD, and GK (all p < 0.001). FW had a greater sweat sodium (Na+) (51.4 ± 9.8 mmol·L-1), whereas GK had the lowest sweat sodium (Na+) (30.9 ± 3.9 mmol·L-1). Hydration strategies should target pre-practice to ensure players are adequately hydrated. Environments deemed to be of moderate risk of hyperthermia significantly elevated the sweat rate but did not influence fluid intake and hydration status compared to low-risk environments. Given the differences in fluid balance and sweat responses, recommendations should be issued relative to soccer position.