The effect of acute caffeine withdrawal on exercise performance in habitual caffeine users

Purpose: The purpose of this study was to investigate how exercise performance is impacted by acute withdrawal from caffeine (CAF) in habitual users and if CAF ingestion will reverse the negative impact of withdrawal or have a net positive benefit. Methods: Ten recreational cyclists (age 39.1 ± 14.9 y; VO2max 54.2 ± 6.2 mL/kg/min) who were habitual CAF consumers (394 ± 146 mg/d) completed four trials, each consisting of peak isokinetic torque testing and a 10-km time trial (TT). On each trial day, subjects consumed either 1.5 mg/kg CAF to prevent withdrawal or placebo (PLA) 8 hours before their laboratory visit, and then 6 mg/kg CAF or PLA one hour prior to exercise. In a randomized counterbalanced design, each subject completed the following treatments: PLA 8 hours pre-exercise + PLA one hour pre-exercise (PLAW), CAF + PLA (PLAN), PLA + CAF (CAFW), CAF + CAF (CAFN). All normally distributed data were assessed using repeated measures ANOVA’s while non-uniform data were assessed non-parametrically using Friedman’s Two-Way ANOVA by Ranks. Results: CAF withdrawal did not impair TT performance (PLAW vs. PLAN p = 0.17). However, pre-exercise CAF ingestion only improved TT performance when compared to the PLAW trial (CAFN vs. PLAW p = 0.014, CAFW vs. PLAW p = 0.01). When withdrawal was mitigated, pre-exercise CAF did not enhance TT performance to pre-exercise PLA (PLAN vs. CAFN p = 0.636). Peak isokinetic torque (30 deg/s) was elevated in the CAFN condition versus the PLAW condition (p = 0.011), with no other differences between conditions. Conclusions: CAF withdrawal does not directly impair exercise performance, and pre-exercise CAF only improves performance when compared to bouts in which withdrawal is being experienced, suggesting that habitual CAF users may not benefit from acute CAF supplementation unless they are experiencing the effects of CAF withdrawal

PRE-LOADED BETAINE IMPROVES THERMOREGULATION WHEN CYCLING IN THE HEAT

BACKGROUND: Heat-related illness compromises health and performance in endurance athletes during training and competition. Betaine (BET) is a nutrient that has been previously identified in animal models to act as an osmolyte and attenuates the effects of thermal stress. However, much of the prior research has only assessed the efficacy of preloading BET in passive heat models. Therefore, the purpose of this study is to examine the effects of preloaded BET in an active heat model. METHODS: Eight endurance-trained males (age 26.4 ± 6.8 years; VO2 Peak 55.5 ± 4.8 mL/kg/min) completed 60 min of cycling at 70% VO2 peak in a hot environment (33° C, 35% RH) after a 7-day supplement loading protocol (50 mg/kg, 2x daily) of placebo (PLA) or BET in a double blind, randomized, counterbalanced, crossover study. Core temperature and thermal sensation were measured at rest and every 10 minutes throughout the active heat protocol. Nude body weight was measured prior to- and immediately post-exercise to calculate sweat rate. No fluid ingestion was allowed during this time. Blood samples were collected at rest, 30 minutes, and immediately after exercise. Visual analog scales were administered before and immediately after exercise to quantify sensations of thirst. Bioelectrical impedance assessed fluid compartments before and after the respective supplementation weeks. RESULTS: Area under curve analysis identified BET as having a smaller overall increase in core body temperature compared to PLA (p = 0.012). Further analysis showed ending core temperature was significantly lower in BET (-0.023 ° C; p = 0.029) than PLA. BET also resulted in a significant increase in sweat rate (mean difference = 0.19 ± 0.20 L/hr; p = 0.02). Blood assessments revealed BET had lower hematocrit at the mid-exercise timepoint compared to PLA (BET: 48.3%; PLA: 50.8%; p = 0.02). Increases in total body water (TBW) and intracellular fluid (ICF) in the BET condition approached significance compared to PLA (TBW: +1.69 L, p = 0.055; ICF: +1.39L, p = 0.066). No significant differences were found between conditions in subjective measures of thermal sensation or thirst (p = 0.318; p = 0.862). CONCLUSION: BET supplementation may have the capacity to mitigate the rise in core body temperature and maintain plasma volume during exercise in an uncompensable heat stress environment, despite having no significant effect on subjective sensations of heat stress

12 WEEKS OF RESISTANCE EXERCISE TRAINING OR ENDURANCE EXERCISE TRAINING HAS NO EFFECT ON ENERGY EXPENDITURE BEFORE, DURING, OR AFTER AN ACUTE BOUT OF WALKING EXERCISE IN SEDENTARY POSTMENOPAUSAL WOMEN WITH OBESITY AND PREDIABETES.

BACKGROUND: Prediabetes, often seen alongside obesity and as a precursor to type 2 diabetes, is prevalent in over 50% of women aged 60 years and above. The metabolic health benefits of exercise are widely acknowledged; however, a clear understanding of metabolic changes induced by resistance training (RT) compared to endurance training (ET) is lacking, particularly in older women. Furthermore, it is unclear what the effects are of 12 weeks of RT or ET training on metabolic activity before, during, and after general physical activities, like walking. OBJECTIVE: To investigate the impacts of 12-week energy-matched RT or ET on energy expenditure before (resting metabolic rate (RMR)), during, and after an acute bout of walking exercise in postmenopausal women with obesity and prediabetes. METHODS: The study included postmenopausal women with obesity and prediabetes that participated in an ongoing larger study of fat metabolism (n =15; mean ± SD: age: 59 ± 6 yrs.; BMI: 35.17. ± 3.53 kg/m2; BF: 46.87 ± 3.94%). Participants were randomized to 12-weeks of ET (n = 7) or RT (n = 8). In addition, six participants (n=3ET, n=3RT) were randomized for an acute bout of low-intensity (50% VO2 peak) treadmill exercise before and after the 12-weeks of training. Energy expenditure before, during, and after an acute bout of exercise at the same absolute intensity were assessed using indirect calorimetry. All study outcomes were assessed before (PRE) and following (POST) 12 weeks of ET or RT. Statistical analyses with Statistical Analysis System (SAS) using marginal models to determine the main effect of time and training (RT or ET) on study outcomes. Post hoc analyses were adjusted for multiple comparisons using the Bonferroni adjustment with α set at 0.05. RESULTS: No differences between study outcomes were present between RT and ET. At POST, as compared to PRE, there were no differences in RMR (n=15; POST: 1496.25 ± 266.66 vs PRE: 1452.30 ± 150.34 kcal/day; p=0.722), exercise energy expenditure (n=6; POST: 228.85 ± 89.77 vs. PRE: 246.98 ± 67.38 kcals; p=0.695) or acute 10 minute post-exercise energy expenditure (n=6; POST: 14.25 ± 2.67 vs. PRE: 16.39 kcal/day; p=0.237). CONCLUSIONS: When the energy expenditure of exercise training is matched, 12 weeks of either ET or RT do not distinctly alter energy expenditure before, during, or after an acute bout of walking exercise in sedentary postmenopausal women with obesity and prediabetes