Effects of reduced frequency breathing on arterial hypoxemia during exercise

The effects of a respiratory training mask on steady-state oxygen consumption at rest and during exercise

No studies have directly measured ventilatory and metabolic responses while wearing a respiratory training mask (RTM) at rest and during exercise. Eleven aerobically fit adults (age: 21 ± 1 years) completed a randomized cross-over study while wearing an RTM or control mask during cycling at 50% Wmax. An RTM was retrofitted with a gas collection tube and set to the manufacturer's "altitude resistance" setting of 6,000 ft (1,800 m). Metabolic gas analysis, ratings of perceived exertion, and oxygen saturation (SpO2) were measured during rest and cycling exercise. The RTM did not affect metabolic, ventilation, and SpO2 at rest compared to the control mask (all, effect of condition: P > 0.05). During exercise, the RTM blunted respiratory rate and minute ventilation (effect of condition: P < 0.05) compared to control. Similar increases in VO2 and VCO2 were observed in both conditions (both, effect of condition: P > 0.05). However, the RTM led to decreased fractional expired O2 and increased fractional expired CO2 (effect of condition: P < 0.05) compared to the control mask. In addition, the RTM decreased SpO2 and increased RPE (both, effect of condition: P < 0.05) during exercise. Despite limited influence on ventilation and metabolism at rest, the RTM reduces ventilation and disrupts gas concentrations during exercise leading to modest hypoxemia.

The Effect of Breathing Patterns Common to Competitive Swimming on Gas Exchange and Muscle Deoxygenation During Heavy-Intensity Fartlek Exercise

During competitive freestyle swimming, the change of direction requires a turn followed by ∼15 m of underwater kicking at various intensities that require a ∼5 s breath-hold (BH). Upon surfacing, breathing must be regulated, as head rotation is necessary to facilitate the breath while completing the length of the pool (∼25 s). This study compared the respiratory and muscle deoxygenation responses of regulated breathing vs. free breathing, during these 25–5 s cycles. It was hypothesized that with the addition of a BH and sprint during heavy-intensity (HVY) exercise, oxygen uptake (VO₂) and oxygen saturation (S_atO₂) would decrease, and muscle deoxygenation ([HHb]) and total hemoglobin ([Hb_tot]) would increase. Ten healthy male participants (24 ± 3 years) performed 4–6 min trials of HVY cycling in the following conditions: (1) continuous free breathing (CONLD); (2) continuous with 5 s BH every 25 s (CONLD-BH); (3) Fartlek (FLK), a 5 s sprint followed by 25 s of HVY; and (4) a combined Fartlek and BH (FLK-BH). Continuous collection of VO₂ and S_atO₂, [Hb_tot], and [HHb] via breath-by-breath gas analysis and near-infrared spectroscopy (normalized to baseline) was performed. Breathing frequency and tidal volumes were matched between CONLD and CONLD-BH and between FLK and FLK-BH. As a result, VO₂ was unchanged between CONLD (2.12 ± 0.35 L/min) and CONLD-BH (2.15 ± 0.42 L/min; p = 0.116) and between FLK (2.24 ± 0.40 L/min) and FLK-BH (2.20 ± 0.45 L/min; p = 0.861). S_atO₂ was higher in CONLD (63 ± 1.9%) than CONLD-BH (59 ± 3.3%; p < 0.001), but was unchanged between FLK (61 ± 2.2%) and FLK-BH (62 ± 3.1%; p = 0.462). Δ[Hb_tot] is higher in CONLD (3.3 ± 1.6 μM) than CONLD-BH (-2.5 ± 1.2 μM; Δ177%; p < 0.001), but was unchanged between FLK (2.0 ± 1.6 μM) and FLK-BH (0.82 ± 1.4 μM; p = 0.979). Δ[HHb] was higher in CONLD (7.3 ± 1.8μM) than CONLD-BH (7.0 ± 2.0μM; Δ4%; p = 0.011) and lower in FLK (6.7 ± 1.8μM) compared to FLK-BH (8.7 ± 2.4 μM; p < 0.001). It is suggested that the unchanged VO₂ between CONLD and CONLD-BH was supported by increased deoxygenation as reflected by decreased Δ[Hb_tot] and blunted Δ[HHb], via apneic-driven redistribution of blood flow away from working muscles, which was reflected by the decreased S_atO₂. However, the preserved VO₂ during FLK-BH vs. FLK has been underpinned by an increase in [HHb].

Exercise with End-expiratory Breath Holding Induces Large Increase in Stroke Volume

Eight well-trained male cyclists participated in two testing sessions each including two sets of 10 cycle exercise bouts at 150% of maximal aerobic power. In the first session, subjects performed the exercise bouts with end-expiratory breath holding (EEBH) of maximal duration. Each exercise bout started at the onset of EEBH and ended at its release (mean duration: 9.6±0.9 s; range: 8.6-11.1 s). At the second testing session, subjects performed the exercise bouts (same duration as in the first session) with normal breathing. Heart rate, left ventricular stroke volume (LVSV), and cardiac output were continuously measured through bio-impedancemetry. Data were analysed for the 4 s preceding and following the end of each exercise bout. LVSV (peak values: 163±33 vs. 124±17 mL, p<0.01) was higher and heart rate lower both in the end phase and in the early recovery of the exercise bouts with EEBH as compared with exercise with normal breathing. Cardiac output was generally not different between exercise conditions. This study showed that performing maximal EEBH during high-intensity exercise led to a large increase in LVSV. This phenomenon is likely explained by greater left ventricular filling as a result of an augmented filling time and decreased right ventricular volume at peak EEBH.

Impact of Hypoventilation Training on Muscle Oxygenation, Myoelectrical Changes, Systemic [K+], and Repeated-Sprint Ability in Basketball Players

This study investigated the impact of repeated-sprint (RS) training with voluntary hypoventilation at low lung volume (VHL) on RS ability (RSA) and on performance in a 30-15 intermittent fitness test (30-15_IFT). Over 4 weeks, 17 basketball players included eight sessions of straight-line running RS and RS with changes of direction into their usual training, performed either with normal breathing (CTL, n = 8) or with VHL (n = 9). Before and after the training, athletes completed a RSA test (12 × 30-m, 25-s rest) and a 30-15_IFT. During the RSA test, the fastest sprint (RSA_best), time-based percentage decrement score (RSA_Sdec), total electromyographic intensity (RMS), and spectrum frequency (MPF) of the biceps femoris and gastrocnemius muscles, and biceps femoris NIRS-derived oxygenation were assessed for every sprint. A capillary blood sample was also taken after the last sprint to analyse metabolic and ionic markers. Cohen's effect sizes (ES) were used to compare group differences. Compared with CTL, VHL did not clearly modify RSA_best, but likely lowered RSA_Sdec (VHL: −24.5% vs. CTL: −5.9%, group difference: −19.8%, ES −0.44). VHL also lowered the maximal deoxygenation induced by sprints ([HHb]_max; group difference: −2.9%, ES −0.72) and enhanced the reoxygenation during recovery periods ([HHb]_min; group difference: −3.6%, ES −1.00). VHL increased RMS (group difference: 18.2%, ES 1.28) and maintained MPF toward higher frequencies (group difference: 9.8 ± 5.0%, ES 1.40). These changes were concomitant with a lower potassium (K⁺) concentration (group difference: −17.5%, ES −0.67), and the lowering in [K⁺] was largely correlated with RSA_Sdec post-training in VHL only (r = 0.66, p < 0.05). However, VHL did not clearly alter PO₂, hemoglobin, lactate and bicarbonate concentration and base excess. There was no difference between group velocity gains for the 30-15_IFT (CTL: 6.9% vs. VHL: 7.5%, ES 0.07). These results indicate that RS training combined with VHL may improve RSA, which could be relevant to basketball player success. This gain may be attributed to greater muscle reoxygenation, enhanced muscle recruitment strategies, and improved K⁺ regulation to attenuate the development of muscle fatigue, especially in type-II muscle fibers.

Severe hypoxemia induced by prolonged expiration and reduced frequency breathing during submaximal swimming

The purpose of this study was to examine the metabolic responses during submaximal swimming with self-selected normal breathing (N) and prolonged expiration along with reduced frequency breathing (RB). Ten male swimmers (age: 23.1 ± 2.2 years; VO₂max: 47.3 ± 7.2 ml · kg^-1 · min^-1) performed 75-, 100-, 175-, 200-, 275-, 300-, 375- and 400-m trials with N and RB at intensity corresponding to 90% of the critical speed. In RB condition, all trials longer than 75 m were interspersed with 25 m of self-selected N in regular intervals. In RB, oxygen saturation during recovery was decreased compared to starting values after 75, 100, 175, 275 and 375 m (78-91%, P < 0.05), while it remained unchanged after all trials in N condition (98 ± 2%, P > 0.05). Lactate concentration was higher in RB than in N after 400 m (4.3 ± 1.5 vs. 3.3 ± 1.7 mmol · l^-1, P < 0.05). During recovery after the 375-m trial, partial pressure of carbon dioxide was increased and pH was decreased in RB compared to N condition. Prolonged expiration along with RB provokes severe hypoxemia during the recovery period after swimming, which is restored with self-selected N during submaximal swimming.

Effects of a 4-week training with voluntary hypoventilation carried out at low pulmonary volumes

This study investigated the effects of training with voluntary hypoventilation (VH) at low pulmonary volumes. Two groups of moderately trained runners, one using hypoventilation (HYPO, n=7) and one control group (CONT, n=8), were constituted. The training consisted in performing 12 sessions of 55 min within 4 weeks. In each session, HYPO ran 24 min at 70% of maximal O(2) consumption ( [V(02max)) with a breath holding at functional residual capacity whereas CONT breathed normally. A V(02max) and a time to exhaustion test (TE) were performed before (PRE) and after (POST) the training period. There was no change in V(O2max), lactate threshold or TE in both groups at POST vs. PRE. At maximal exercise, blood lactate concentration was lower in CONT after the training period and remained unchanged in HYPO. At 90% of maximal heart rate, in HYPO only, both pH (7.36+/-0.04 vs. 7.33+/-0.06; p<0.05) and bicarbonate concentration (20.4+/-2.9 mmolL(-1) vs. 19.4+/-3.5; p<0.05) were higher at POST vs. PRE. The results of this study demonstrate that VH training did not improve endurance performance but could modify the glycolytic metabolism. The reduced exercise-induced blood acidosis in HYPO could be due to an improvement in muscle buffer capacity. This phenomenon may have a significant positive impact on anaerobic performance.

Prolonged expiration down to residual volume leads to severe arterial hypoxemia in athletes during submaximal exercise

The goal of this study was to assess the effects of a prolonged expiration (PE) carried out down to the residual volume (RV) during a submaximal exercise and consider whether it would be worth including this respiratory technique in a training programme to evaluate its effects on performance. Ten male triathletes performed a 5-min exercise at 70% of maximal oxygen consumption in normal breathing (NB(70)) and in PE (PE(70)) down to RV. Cardiorespiratory parameters were measured continuously and an arterialized blood sampling at the earlobe was performed in the last 15s of exercise. Oxygen consumption, cardiac frequency, end-tidal and arterial carbon dioxide pressure, alveolar-arterial difference for O(2) (PA(O2) - Pa(O2)) and P(50) were significantly higher, and arterial oxygen saturation (87.4+/-3.4% versus 95.0+/-0.9%, p<0.001), alveolar (PA(O2)) or arterial oxygen pressure, pH and ventilatory equivalent were significantly lower in PE(70) than NB(70). There was no difference in blood lactate between exercise modalities. These results demonstrate that during submaximal exercise, a prolonged expiration down to RV can lead to a severe hypoxemia caused by a PA(O2) decrement (r=0.56; p<0.05), a widened PA(O2) - Pa(O2) (r=-0.85; p<0.001) and a right shift of the oxygen dissociation curve (r=-0.73; p<0.001).

Influence of different rest intervals during active or passive recovery on repeated sprint swimming performance

The purpose of this study was to investigate the effect of active or passive recovery after two different rest intervals on performance during repeated bouts of maximal swimming exercise. Sixteen swimmers (eight males and eight females) performed four trials in a counterbalanced order. Eight repetitions of 25-m sprints (8 x 25 m), with a rest interval of 45 or 120 s, followed by a 50-m sprint test 6 min later, were performed in each trial. The 45 or 120-s interval was either active (A45 and A120) or passive (P45 and P120). The intensity of the active recovery corresponded to 60% of the individual best 100-m velocity. Performance time was recorded using an official competition timing system. The first 25-m sprint was comparable across trials (P>0.05), but performance was decreased after the second sprint during active compared to passive recovery, irrespective of the interval duration (P<0.05). The 50-m sprint time was 2.4% better in the P120 and A120 compared to the A45 and P45 trials (P<0.05). After completing the 8x25 m, blood lactate was decreased with active recovery when the interval period was 120 s (P120 vs A120, P<0.05). Blood lactate concentration at the start as well as 5 min after the 50-m sprint was lower in the A120 and A45 compared to the P120 and P45 trials respectively (P<0.05). Plasma glycerol was not different between trials (P>0.05), whereas plasma ammonia was higher in the A45 compared to the P120 trial (P<0.05). The interval period separating short-duration sprints may therefore alter performance when subsequent maximum exertion is applied. For sustained sprinting ability, passive recovery is advised during repeated swimming sprints of short duration.

Metabolic consequences of reduced frequency breathing during submaximal exercise at moderate altitude

The intention of this study was to determine the metabolic consequences of reduced frequency breathing (RFB) at total lung capacity (TLC) in competitive cyclists during submaximal exercise at moderate altitude (1520 m; barometric pressure, PB = 84.6 kPa; 635 mm Hg). Nine trained males performed an RFB exercise test (10 breaths.min-1) and a normal breathing exercise test at 75-85% of the ventilatory threshold intensity for 6 min on separate days. RFB exercise induced significant (P less than 0.05) decreases in ventilation (VE), carbon dioxide production (VCO2), respiratory exchange ratio (RER), ventilatory equivalent for O2 consumption (VE/VO2), arterial O2 saturation and increases in heart rate and venous lactate concentration, while maintaining a similar O2 consumption (VO2). During recovery from RFB exercise (spontaneous breathing) a significant (P less than 0.05) decreases in blood pH was detected along with increases in VE, VO2, VCO2, RER, and venous partial pressure of carbon dioxide. The results indicate that voluntary hypoventilation at TLC, during submaximal cycling exercise at moderate altitude, elicits systemic hypercapnia, arterial hypoxemia, tissue hypoxia and acidosis. These data suggest that RFB exercise at moderate altitude causes an increase in energy production from glycolytic pathways above that which occurs with normal breathing.

Delayed appearance of blood lactate with reduced frequency breathing during exercise

The purpose of the present study was to investigate the blood lactate (LA-) responses to hypoventilation induced by reduced frequency breathing (RFB) during recovery from exercise. Five male subject performed 16 4 min cycling bouts alternating with 16 min rest periods. Exercise intensities were chosen at power outputs corresponding to 30% VO2max at 2 mMLA-, VO2 at 4 mMLA-, and 90% VO2max in each subject. Breathing frequency was voluntarily controlled starting 10 s before each 3rd min of exercise and maintained throughout the rest of the exercise period. Four different breathing patterns at each exercise intensity were used: normal breathing (NB), breathing every 4 s, breathing every 8 s, and maximal RFB. Except for the NB trials, subjects held their breath at functional residual capacity during each breathing interval. The concentration difference of LA- between the 3rd min sample and the 4th min sample was defined as the lactate change during exercise (delta LA-ex), and that between the 4th min sample and the sample at the 3rd min after the end of the exercise as the lactate change during recovery (delta LA-rec). An ANOVA showed significant (p less than 0.05) differences in breathing procedures only in delta LA-rec. delta LA-rec seemed to increase as compared to NB only at VO2 at 4 mMLA- and 90% VO2max, while delta LA-ex remained unchanged as compared to NB in spite of reduced VA. These results might indicate that RFB inhibited lactate removal from working muscles during exercise.