We examined the validity and reliability of the Apple Watch heart rate sensor during and in recovery from exercise. Twenty-one males completed treadmill exercise while wearing two Apple Watches (left and right wrists) and a Polar S810i monitor (criterion). Exercise involved 5-min bouts of walking, jogging, and running at speeds of 4 km.h −1 , 7 km.h −1 , and 10 km.h −1 , followed by 11 min of rest between bouts. At all exercise intensities the mean bias was trivial. There were very good correlations with the criterion during walking (L: r=0.97; R: r=0.97), but good (L: r=0.93; R: r=0.92) and poor/good (L: r=0.81; R: r=0.86) correlations during jogging and running. Standardised typical error of the estimate was small, moderate, and moderate to large. There were good correlations following walking, but poor correlations following jogging and running. The percentage of heart rates recorded reduced with increasing intensity but increased over time. Intra-device standardised typical errors decreased with intensity. Inter-device standardised typical errors were small to moderate with very good to nearly perfect intraclass correlations. The Apple Watch heart rate sensor has very good validity during walking but validity decreases with increasing intensity.

The purpose of the present investigation was to observe the ergogenic potential of 0.3 g·kg-1 of sodium bicarbonate (NaHCO3) in competitive, nonelite swimmers using a repeated swim sprint design that eliminated the technical component of turning. Six male (181.2 ± 7.2 cm; 80.3 ± 11.9 kg; 50.8 ± 5.5 ml·kg-1·min-1 VO2max) and 8 female (168.8 ± 5.6 cm; 75.3 ± 10.1 kg; 38.8 ± 2.6 ml·kg-1·min-1 VO2max) swimmers completed 2 trial conditions (NaHCO3 [BICARB] and NaCl placebo [PLAC]) implemented in a randomized (counterbalanced), single blind manner, each separated by 1 week. Swimmers were paired according to ability and completed 8, 25-m front crawl maximal effort sprints each separated by 5 seconds. Blood acid-base status was assessed preingestion, pre, and postswim via capillary finger sticks, and total swim time was calculated as a performance measure. Total swim time was significantly decreased in the BICARB compared to PLAC condition (p = 0.04), with the BICARB condition resulting in a 2% decrease in total swim time compared to the PLAC condition (159.4 ± 25.4 vs. 163.2 ± 25.6 seconds; mean difference = 4.4 seconds; 95% confidence interval = 8.7-0.1). Blood analysis revealed significantly elevated blood buffering potential preswim (pH: BICARB = 7.48 ± 0.01, PLAC = 7.41 ± 0.01) along with a significant decrease in extracellular K+ (BICARB = 4.0 ± 0.1 mmol·L-1, PLAC = 4.6 ± 0.1 mmol·L-1). The findings suggest that 0.3 g·kg-1 NaHCO3 ingested 2.5 hours before exercise enhances the blood buffering potential and may positively influence swim performance.

Change in estimated VO derived from the ACSM leg cycling equation is not an accurate surrogate for directly determined changes in VO . Our findings show poor agreement between estimates of VO and directly determined VO . Applying estimates of VO to determine CRF change may over-estimate the efficacy of CR and lead to a different interpretation of study findings.

IntroductionInvestigate the effectiveness of short-term heat acclimation (STHA), over 5-days (permissive dehydration), on an intermittent sprint exercise protocol (HST) with females. Controlling for menstrual cycle phase.Materials and MethodsTen, moderately trained, females (Mean [SD]; age 22.6 [2.7] y; stature 165.3 [6.2] cm; body mass 61.5 [8.7] kg; V.⁢O2⁢peak 43.9 [8.6] mL⋅kg–1⋅min–1) participated. The HST (31.0°C; 50%RH) was 9 × 5 min (45-min) of intermittent exercise, based on exercise intensities of female soccer players, using a motorized treadmill and Wattbike. Participants completed HST1 vs. HST2 as a control (C) trial. Followed by 90 min, STHA (no fluid intake), for five consecutive days in 39.5°C; 60%RH, using controlled-hyperthermia (∼rectal temperature [Tre] 38.5°C). The HST3 occurred within 1 week after STHA. The HST2 vs HST3 trials were in the luteal phase, using self-reported menstrual questionnaire and plasma 17β-estradiol.ResultsPre (HST2) vs post (HST3) STHA there was a reduction at 45-min in Tre by 0.20°C (95%CI −0.30 to −0.10°C; d = 0.77); T¯s⁢k (−0.50; −0.90 to −0.10°C; d = 0.80); and T¯b (−0.25; −0.35 to −0.15°C; d = 0.92). Cardiac frequency reduced at 45-min (−8; −16 to −1 b⋅min–1; d = 1.11) and %PV increased (7.0; −0.4 to 14.5%: d = 1.27). Mean power output increased across all nine maximal sprints by 56W (−26 to 139W; d = 0.69; n = 9). There was limited difference (P > 0.05) for these measures in HST1 vs HST2 C trial.DiscussionShort-term heat acclimation (5-days) using controlled-hyperthermia, leads to physiological adaptation during intermittent exercise in the heat, in moderately trained females when controlling for menstrual cycle phase.

Purpose High-intensity interval training (HIIT) and circuit training (CT) are popular methods of exercise, eliciting improvements in cardiorespiratory fitness (CRF). However, direct comparisons of these two training methods are limited. We investigated the effects of HIIT and CT on CRF. Methods Thirty-nine apparently healthy middle-aged participants [HIIT; mean age: 42.5 ± 12.3; V O 2max 31.5 ± 7.1 (ml kg −1 min −1); 52% males; CT; mean age: 41.2 ± 12.9; V O 2max 31.4 ± 6.8 (ml kg −1 min −1); 57% males] were randomly allocated to two sessions per week of HIIT or CT over 8 weeks. HIIT performed ten 1-min cycle-ergometry intervals at > 85% HR max , separated by ten 1-min intervals of active recovery. The CT group performed up to 40-min of CT at 60-80% HR max. CRF was measured using maximum oxygen uptake (V O 2max), ventilatory anaerobic threshold (V O 2 at VAT) and maximum oxygen pulse (V O 2 /HR). Results V O 2max increased by 12% following HIIT