The authors examined whether changes in heart-rate (HR) variability (HRV) could consistently track adaptation to training and race performance during a 32-wk competitive season. An elite male long-course triathlete recorded resting HR (RHR) each morning, and vagal-related indices of HRV (natural logarithm of the square root of mean squared differences of successive R−R intervals [ln rMSSD] and the ratio of ln rMSSD to R−R interval length [ln rMSSD:RR]) were assessed. Daily training load was quantified using a power meter and wrist-top GPS device. Trends in HRV indices and training load were examined by calculating standardized differences (ES). The following trends in week-to-week changes were consistently observed: (1) When the triathlete was coping with a training block, RHR decreased (ES −0.38 [90% confidence limits −0.05;−0.72]) and ln rMSSD increased (+0.36 [0.71;0.00]). (2) When the triathlete was not coping, RHR increased (+0.65 [1.29;0.00]) and ln rMSSD decreased (−0.60 [0.00;−1.20]). (3) Optimal competition performance was associated with moderate decreases in ln rMSSD (−0.86 [−0.76;−0.95]) and ln rMSSD:RR (−0.90 [−0.60;−1.20]) in the week before competition. (4) Suboptimal competition performance was associated with small decreases in ln rMSSD (−0.25 [−0.76;−0.95]) and trivial changes in ln rMSSD:RR (−0.04 [0.50;−0.57]) in the week before competition. To conclude, in this triathlete, a decrease in RHR concurrent with increased ln rMSSD compared with the previous week consistently appears indicative of positive training adaptation during a training block. A simultaneous reduction in ln rMSSD and ln rMSSD:RR during the final week preceding competition appears consistently indicative of optimal performance.
Jamie Stanley, Shaun D’Auria and Martin Buchheit
Samuel T Tebeck, Jonathan D Buckley, Clint R Bellenger and Jamie Stanley
To investigate the effect of a 5-day short-term heat acclimation (STHA) protocol in dry (43˚C and 20 % RH) or humid (32˚C and 80 % RH) environmental conditions on endurance cycling performance in temperate conditions (21˚C).
In a randomised, cross-over design, eleven cyclists completed each of the two, 5-day blocks of STHA matched for heat index (44˚C) and total exposure time (480 min), separated by 30-days. Pre- and post-temperate endurance performance (4-min mean max power, lactate threshold 1 and 2) was assessed in addition a heat stress test used to assess individual levels of heat adaptation.
Differences in endurance performance were unclear. Following dry STHA, gross mechanical efficiency was likely reduced [between-condition effect size dry vs humid (90 % confidence interval) [-0.59 (-1.05, -0.15)], oxygen uptake was likely increased for a given workload [+0.64 (0.14, 1.07)] and energy expenditure likely increased [+0.59 (0.17, 1.03)]. Plasma volume expansion at Day 5 of acclimation was similar (within-condition outcome +4.6 ± 6.3 % and +5.3 ± 5.1 % dry and humid respectively) but was retained for 3-4 days longer after the final humid STHA exposure (-0.2 ± 8.1 % and +4.5 ± 4.2 % dry and humid respectively). Sweat rate was very likely increased during dry STHA [+0.57 (0.25, 0.89)] and possibly increased [+0.18 (-0.15; 0.50)] during humid STHA.
STHA induced divergent adaptations between dry and humid conditions, but did not result in differences in temperate endurance performance.
Avish P. Sharma, Philo U. Saunders, Laura A. Garvican-Lewis, Brad Clark, Jamie Stanley, Eileen Y. Robertson and Kevin G. Thompson
To determine the effect of training at 2100-m natural altitude on running speed (RS) during training sessions over a range of intensities relevant to middle-distance running performance.
In an observational study, 19 elite middle-distance runners (mean ± SD age 25 ± 5 y, VO2max, 71 ± 5 mL · kg–1 · min–1) completed either 4–6 wk of sea-level training (CON, n = 7) or a 4- to 5-wk natural altitude-training camp living at 2100 m and training at 1400–2700 m (ALT, n = 12) after a period of sea-level training. Each training session was recorded on a GPS watch, and athletes also provided a score for session rating of perceived exertion (sRPE). Training sessions were grouped according to duration and intensity. RS (km/h) and sRPE from matched training sessions completed at sea level and 2100 m were compared within ALT, with sessions completed at sea level in CON describing normal variation.
In ALT, RS was reduced at altitude compared with sea level, with the greatest decrements observed during threshold- and VO2max-intensity sessions (5.8% and 3.6%, respectively). Velocity of low-intensity and race-pace sessions completed at a lower altitude (1400 m) and/or with additional recovery was maintained in ALT, though at a significantly greater sRPE (P = .04 and .05, respectively). There was no change in velocity or sRPE at any intensity in CON.
RS in elite middle-distance athletes is adversely affected at 2100-m natural altitude, with levels of impairment dependent on the intensity of training. Maintenance of RS at certain intensities while training at altitude can result in a higher perceived exertion.