Martin Buchheit

Effect of cold or thermoneutral water immersion on post-exercise heart rate recovery and heart rate variability indices

This study aimed to investigate the effect of cold and thermoneutral water immersion on post-exercise parasympathetic reactivation, inferred from heart rate (HR) recovery (HRR) and HR variability (HRV) indices. Twelve men performed, on three separate occasions, an intermittent exercise bout (all-out 30-s Wingate test, 5 min seated recovery, followed by 5 min of submaximal running exercise), randomly followed by 5 min of passive (seated) recovery under either cold (CWI), thermoneutral water immersion (TWI) or control (CON) conditions. HRR indices (e.g., heart beats recovered in the first minute after exercise cessation, HRR(60)(s)) and vagal-related HRV indices (i.e., natural logarithm of the square root of the mean of the sum of the squares of differences between adjacent normal R-R intervals (Ln rMSSD)) were calculated for the three recovery conditions. HRR(60)(s) was faster in water immersion compared with CON conditions [30+/-9 beats min(-)(1) for CON vs. 43+/- 10 beats min(-)(1) for TWI (P=0.003) and 40+/-13 beats min(-)(1) for CWI (P=0.017)], while no difference was found between CWI and TWI (P=0.763). Ln rMSSD was higher in CWI (2.32+/-0.67 ms) compared with CON (1.98+/-0.74 ms, P=0.05) and TWI (2.01+/-0.61 ms, P=0.08; aES=1.07) conditions, with no difference between CON and TWI (P=0.964). Water immersion is a simple and efficient means of immediately triggering post-exercise parasympathetic activity, with colder immersion temperatures likely to be more effective at increasing parasympathetic activity.

Repeated sprints with directional changes: do angles matter?

Abstract To examine whether performance, physiological and perceptual responses to repeated sprints including changes of direction are angle-dependent, twelve team-sport players performed (1) single 30-m sprints without or with two (45°, 90° or 135°) changes of direction and (2) repeated-sprint sequences matched for initial sprint time without (Line [6x30m]) or with (45° [6x28.0m], 90° [6x22.2m] or 135° [6x19.5m]) two changes of direction. For each sequence, mean sprint time (RSmean), peak heart rate (HRpeak), blood lactate concentration (Δ[La]b) and rating of perceived exertion (RPE) were recorded. Results show that performance, physiological and perceptual responses were angle-dependent. Compared with Line, RSmean was likely lower for 45˚ (−1.7%(90%CL:−3.5;0.1); chances for greater/similar/lower values of 1/23/76%, respectively) and possibly greater for 135˚ (+0.8%(90%CL:−0.6;2.3), 44/53/3%). HRpeak, Δ[La]b and RPE were likely greater for Line compared with the three other protocols. RPE during 45˚ was greater than during 90˚(+14%(90%CL:8;19), 0/1/99%) and 135˚ (+11%(90%CL:1;22), 2/15/83%). The correlation coefficients describing the relationships between the four single 30-m sprints were <0.70; these for RSmean times were >0.70. Performance, physiological and perceptual response during repeated sprints with changes of direction are angle-dependent. However, unlike changes of direction speed, repeated-sprint ability with changes of direction is more likely to be a general quality.

Static apnea effect on heart rate and its variability in elite breath-hold divers

BACKGROUND The diving response includes cardiovascular adjustments known to decrease oxygen uptake and thus prolong apnea duration. As this diving response is in part characterized by a pronounced decrease in heart rate (HR), it is thought to be vagally mediated. METHODS In five professional breath-hold divers (BHDs) and five less-trained controls (CTL), we investigated whether the diving response is in fact associated with an increase in the root mean square successive difference of the R-R intervals (RMSSD), a time-domain heart rate variability (HRV) index. HR behavior and arterial oxygen saturation (SaO2) were continuously recorded during one maximal apnea. Short-term changes in SaO2, HR, and RMSSD were calculated over the complete apnea duration. RESULTS BHDs presented bi-phasic HR kinetics, with two HR decreases (32 +/- 17% and 20 +/- 10% of initial HR). The second HR decrease, which was concomitant to the pronounced SaO2 decrease, was also simultaneous to a marked increase in RMSSD. CTL showed only one HR decrease (50 +/- 10% of initial HR), which appeared before the concomitant SaO2 and RMSSD changes. When all subject data were combined, arterial desaturation was positively correlated with total apnea time (r = 0.87, P < 0.01). CONCLUSION This study indicates that baroreflex stimulation and hypoxia may be involved in the bi-phasic HR response of BHDs and thus in their longer apnea duration.