Stylianos N. Kounalakis

Muscle and cerebral oxygenation during exercise performance after short-term respiratory work.

The purpose of the study was to investigate the effect of 30-min voluntary hyperpnoea on cerebral, respiratory and leg muscle balance between O(2) delivery and utilization during a subsequent constant-power test. Eight males performed a V˙O(2max) test, and two exercise tests at 85% of peak power output: (a) a control constant-power test (CPT), and (b) a constant-power test after a respiratory maneuver (CPT(RM)). Oxygenated (Δ[O(2)Hb]), deoxygenated (Δ[HHb]) and total (Δ[tHb]) hemoglobin in cerebral, intercostal and vastus lateralis were monitored with near-infrared spectroscopy. The performance time dropped ∼15% in CPT(RM) (6:55±2:52min) compared to CPT (8:03±2:33min), but the difference was not statistically significant. The vastus lateralis and intercostal Δ[tHb] and Δ[HHb] were lower in CPT(RM) than in CPT (P≤0.05). There were no differences in cerebral oxygenation between the trials. Thus, respiratory work prior to an exercise test influences the oxygenation during exercise in the leg and respiratory muscles, but not in the frontal cortex.

The Effect of Normobaric Hypoxic Confinement on Metabolism, Gut Hormones, and Body Composition

To assess the effect of normobaric hypoxia on metabolism, gut hormones, and body composition, 11 normal weight, aerobically trained (O2peak: 60.6 ± 9.5 ml·kg−1·min−1) men (73.0 ± 7.7 kg; 23.7 ± 4.0 years, BMI 22.2 ± 2.4 kg·m−2) were confined to a normobaric (altitude ≃ 940 m) normoxic (NORMOXIA; PIO2 ≃ 133.2 mmHg) or normobaric hypoxic (HYPOXIA; PIO was reduced from 105.6 to 97.7 mmHg over 10 days) environment for 10 days in a randomized cross-over design. The wash-out period between confinements was 3 weeks. During each 10-day period, subjects avoided strenuous physical activity and were under continuous nutritional control. Before, and at the end of each exposure, subjects completed a meal tolerance test (MTT), during which blood glucose, insulin, GLP-1, ghrelin, peptide-YY, adrenaline, noradrenaline, leptin, and gastro-intestinal blood flow and appetite sensations were measured. There was no significant change in body weight in either of the confinements (NORMOXIA: −0.7 ± 0.2 kg; HYPOXIA: −0.9 ± 0.2 kg), but a significant increase in fat mass in NORMOXIA (0.23 ± 0.45 kg), but not in HYPOXIA (0.08 ± 0.08 kg). HYPOXIA confinement increased fasting noradrenaline and decreased energy intake, the latter most likely associated with increased fasting leptin. The majority of all other measured variables/responses were similar in NORMOXIA and HYPOXIA. To conclude, normobaric hypoxic confinement without exercise training results in negative energy balance due to primarily reduced energy intake.

Cardiovascular drift and cerebral and muscle tissue oxygenation during prolonged cycling at different pedalling cadences.

We hypothesized that a faster cycling cadence could exaggerate cardiovascular drift and affect muscle and cerebral blood volume and oxygenation. Twelve healthy males (mean age, 23.4 ± 3.8 years) performed cycle ergometry for 90 min on 2 separate occasions, with pedalling frequencies of 40 and 80 r·min(-1), at individual workloads corresponding to 60% of their peak oxygen consumption. The main measured variables were heart rate, ventilation, cardiac output, electromyographic activity of the vastus lateralis, and regional muscle and cerebral blood volume and oxygenation. Cardiovascular drift developed at both cadences, but it was more pronounced at the faster than at the slower cadence, as indicated by the drop in cardiac output by 1.0 ± 0.2 L·min(-1), the decline in stroke volume by 9 ± 3 mL·beat(-1), and the increase in heart rate by 9 ± 1 beats·min(-1) at 80 r·min(-1). At the faster cadence, minute ventilation was higher by 5.0 ± 0.5 L·min(-1), and end-tidal CO(2) pressure was lower by 2.0 ± 0.1 torr. Although higher electromyographic activity in the vastus lateralis was recorded at 80 r·min(-1), muscle blood volume did not increase at this cadence, as it did at 40 r·min(-1). In addition, muscle oxygenation was no different between cadences. In contrast, cerebral regional blood volume and oxygenation at 80 r·min(-1) were not as high as at 40 r·min(-1) (p < 0.05). Faster cycling cadence exaggerates cardiovascular drift and seems to influence muscle and cerebral blood volume and cerebral oxygenation, without muscle oxygenation being radically affected.

Forearm–finger skin temperature gradient as an index of cutaneous perfusion during steady-state exercise

The purpose of this study was to examine whether the forearm–finger skin temperature gradient (Tforearm–finger), an index of vasomotor tone during resting conditions, can also be used during steady‐state exercise. Twelve healthy men performed three cycling trials at an intensity of ~60% of their maximal oxygen uptake for 75 min separated by at least 48 h. During exercise, forearm skin blood flow (BFF) was measured with a laser‐Doppler flowmeter, and finger skin blood flow (PPG) was recorded from the left index fingertip using a pulse plethysmogram. Tforearm–finger of the left arm was calculated from the values derived by two thermistors placed on the radial side of the forearm and on the tip of the middle finger. During exercise, PPG and BFF increased (P<0·001), and Tforearm–finger decreased (P<0·001) from their resting values, indicating a peripheral vasodilatation. There was a significant correlation between Tforearm–finger and both PPG (r = −0·68; P<0·001) and BFF (r = −0·50; P<0·001). It is concluded that Tforearm–finger is a valid qualitative index of cutaneous vasomotor tone during steady‐state exercise.

Oxygen saturation in the triceps brachii muscle during an arm Wingate test: the role of training and power output.

The purpose of this study was to investigate the role of training and power output on muscle oxygen desaturation during and resaturation after an arm Wingate test (WAnT). Two groups of subjects were studied; the first group consisted of nine athletes participating in upper arm anaerobic sports and the second group of 11 university students. As a consequence, the group of athletes (HP) produced higher peak and mean power output (p < 0.01) than the group of university students (LP). Muscle oxygenation status was evaluated by using near infrared spectroscopy at the triceps brachii. The HP group exhibited 17.6 ± 8.0% less muscle oxygen desaturation than the LP group (p < 0.05) but similar muscle total hemoglobin during exercise and faster (p < 0.05) muscle oxygen resaturation during recovery (τ = 12.4 ± 5.2 sec in HP vs. τ = 24.2 ± 11.0 sec in LP). These results indicate that the HP group exhibits less muscle desaturation during an arm WAnT and has a faster resaturation rate, probably attributed to differences in muscle mass, muscle fiber recruitment capability, and ATP production through anaerobic pathways.

The Effect of a Sleep High–Train Low Regimen on the Finger Cold-Induced Vasodilation Response

The present study evaluated the effect of a sleep high-train low regimen on the finger cold-induced vasodilation (CIVD) response. Seventeen healthy males were assigned to either a control (CON; n=9) or experimental (EXP; n=8) group. Each group participated in a 28-day aerobic training program of daily 1-h exercise (50% of peak power output). During the training period, the EXP group slept at a simulated altitude of 2800 meters (week 1) to 3400 m (week 4) above sea level. Normoxic (CIVD(NOR); CON and EXP groups) and hypoxic (CIVD(HYPO); F(I)O(2)=0.12; EXP group only) CIVD characteristics were assessed before and after the training period during a 30-min immersion of the hand in 8°C water. After the intervention, the EXP group had increased average finger skin temperature (CIVD(NOR): +0.5°C; CIVD(HYPO): +0.5°C), number of waves (CIVD(NOR): +0.5; CIVD(HYPO): +0.6), and CIVD amplitude (CIVD(NOR): +1.5°C; CIVD(HYPO): +3°C) in both CIVD tests (p<0.05). In contrast, the CON group had an increase in only the CIVD amplitude (+0.5°C; p<0.05). Thus, the enhancement of aerobic performance combined with altitude acclimatization achieved with the sleep high-train low regimen contributed to an improved finger CIVD response during cold-water hand immersion in both normoxic and hypoxic conditions.

Peak oxygen uptake and regional oxygenation in response to a 10-day confinement to normobaric hypoxia.

We investigated the effect of hypoxic acclimatization per se, without any concomitant influence of strenuous physical activity on muscle and cerebral oxygenation. Eight healthy male subjects participated in a crossover‐designed study. In random order, they conducted a 10‐day normoxic (CON) and a 10‐day hypoxic (EXP) confinement. Pre and post both CON and EXP confinements, subjects conducted two incremental‐load cycling exercises to exhaustion; one under normoxic, and the other under hypoxic (FIO2 = 0.154) conditions. Oxygen uptake ( V ˙ O 2 ), ventilation ( V ˙ E ), and relative changes in regional hemoglobin oxygenation (Δ([HbO2]) in the cerebral cortex and in the serratus anterior (SA) and vastus lateralis (VL) muscles were measured. No changes were observed in the CON confinement. Peak work rate and V ˙ O 2 p ⁢ e a k were similar pre and post in the EXP confinement, whereas V ˙ E increased in the EXP post normoxic and hypoxic trials (P < 0.05). The exercise‐induced drop in VL Δ[HbO2] was less in the post‐ than pre‐EXP trial by 4.0 ± 0.4 and 4.2 ± 0.6 μM during normoxic and hypoxic exercise, respectively. No major changes were observed in cerebral or SA oxygenation. These results demonstrate that a 10‐day hypoxic exposure without any concomitant physical activity had no effect on normoxic or hypoxic V ˙ O 2 p ⁢ e a k , despite the enhanced VL oxygenation.

Intermittent Normobaric Hypoxic Exposures at Rest : Effects on Performance in Normoxia and Hypoxia

INTRODUCTION It has been speculated that short (-1-h) exposures to intermittent normobaric hypoxia at rest can enhance subsequent exercise performance. Thus, the present study investigated the effect of daily resting intermittent hypoxic exposures (IHE) on peak aerobic capacity and performance under both normoxic and hypoxic conditions. METHODS Eighteen subjects were equally assigned to either a control (CON) or IHE group and performed a 4-wk moderate intensity cycling exercise training (1 h x d(-1), 5 d x wk(-1)). The IHE group additionally performed IHE (60 min) prior to exercise training. IHE consisted of seven cycles alternating between breathing a hypoxic gas mixture (5 min; F1O2 = 0.12-0.09) and room air (3 min; F1O2 = 0.21). Normoxic and hypoxic peak aerobic capacity (VO2(peak)) and endurance performance were evaluated before (PRE), during (MID), upon completion (POST), and 10 d after (AFTER) the training period. RESULTS Similar improvements were observed in normoxic VO2(peak) tests in both groups [IHE: delta(POST-PRE) = +10%; CON: delta(POST-PRE) = + 14%], with no changes in the hypoxic condition. Both groups increased performance time in the normoxic constant power test only [IHE: delta(POST-PRE) = +108%; CON: delta(POST-PRE) = +114%], whereas only the IHE group retained this improvement in the AFTER test. Higher levels of minute ventilation were noted in the IHE compared to the CON group at the POST and AFTER tests. CONCLUSION Based on the results of this study, the IHE does not seem to be beneficial for normoxic and hypoxic performance enhancement.

Carbon monoxide exposure during exercise performance: muscle and cerebral oxygenation

Aim:  To investigate the effect of carbon monoxide (CO) in the inspired air as anticipated during peak hours of traffic in polluted megalopolises on cerebral, respiratory and leg muscle oxygenation during a constant‐power test (CPT). In addition, since O2 breathing is used to hasten elimination of CO from the blood, we examined the effect of breathing O2 following exposure to CO on cerebral and muscle oxygenation during a subsequent exercise test under CO conditions.

Effects of Two Short-Term, Intermittent Hypoxic Training Protocols on the Finger Temperature Response to Local Cold Stress

The study examined the effects of two short-term, intermittent hypoxic training protocols, namely exercising in hypoxia and living in normoxia (LL-TH; n=8), and exercising in normoxia preceded by a series of brief intermittent hypoxic exposures at rest (IHE+NOR; n=8), on the finger temperature response during a sea-level local cold test. In addition, a normoxic group was assigned as a control group (NOR; n=8). All groups trained on a cycle-ergometer 1 h/day, 5 days/week for 4 weeks at 50% of peak power output. Pre, post, and 11 days after the last training session, subjects immersed their right hand for 30 min in 8°C water. In the NOR group, the average finger temperature was higher in the post (+2.1°C) and 11-day after (+2.6°C) tests than in the pre-test (p≤0.001). Conversely, the fingers were significantly colder immediately after both hypoxic protocols (LL-TH: -1.1°C, IHE+NOR: -1.8°C; p=0.01). The temperature responses returned to the pre-training level 11 days after the hypoxic interventions. Ergo, present findings suggest that short-term intermittent hypoxic training impairs sea-level local cold tolerance; yet, the hypoxic-induced adverse responses seem to be reversible within a period of 11 days.