Effects of High-Intensity Inspiratory Muscle Warm-Up on High-Intensity Exercise Performance and Muscle Oxygenation

PURPOSE

An inspiratory muscle warm-up (IMW) improves inspiratory muscle function, but the effects of high-intensity exercise are inconsistent. We aimed to determine the effects of high-intensity IMW on high-intensity exercise performance and muscle oxygenation.

METHODS

Ten healthy men (maximal oxygen uptake [V˙O2max] 52.2 [5.0] mL·kg-1·min-1) performed constant-load exercise to exhaustion on a cycle ergometer at V˙O2max under 2 IMW conditions: a placebo condition (PLA) and a high-intensity IMW condition (HIGH). The inspiratory loads were set at 15% and 80% of maximal inspiratory pressure, respectively. Maximal inspiratory pressure was measured before and after IMW. Oxyhemoglobin was measured in the vastus lateralis by near-infrared spectroscopy during exercise. Rating of perceived exertion (RPE) for a leg was measured after 1 and 2 minutes of exercise.

RESULTS

Exercise tolerance was significantly higher under HIGH than PLA (228 [49] s vs 218 [49] s, P = .003). Maximal inspiratory pressure was significantly increased by IMW under HIGH (from 125 [20] to 136 [25] cm H2O, P = .031). Oxyhemoglobin was significantly higher under HIGH than PLA at 80% of the total duration of exercise (P = .048). RPE for the leg was significantly lower under HIGH than PLA after 2 minutes of exercise (P = .019).

CONCLUSIONS

Given that oxyhemoglobin is an index of local oxygen supply, the results of this study suggest that high-intensity IMW increases the oxygen supply to active limbs. It may also reflect a reduction in RPE in the leg. In addition, high-intensity IMW may improve exercise performance.

Effects of 7-day quercetin intervention on motor unit activity and muscle contractile properties before and after resistance exercise in young adults randomized controlled trials

We investigated whether the alteration of the motor unit recruitment threshold (MURT) caused by quercetin ingestion intervention for 7 days modifies motor unit activation patterns before and after a single session of resistance exercise. Twenty young male and female adults were divided into two groups: ingestion of placebo (PLA) or quercetin glycosides at 200 mg/day (QUE). High-density surface electromyography during submaximal contractions was measured to assess the motor unit firing rate (MUFR) and MURT of the vastus lateralis muscle before (PRE) and after (POST) resistance exercise (DAY1). The same measurements were repeated after 7 days of placebo or quercetin glycoside ingestion (DAY8). In QUE, MURT decreased more from DAY1-PRE to DAY8-PRE (29.1 ± 9.1 to 27.1 ± 9.5% MVC, p < 0.001) but not in PLA (29.8 ± 10.4 to 28.9 ± 9.7% MVC, p < 0.167). For percentage change in MUFR following resistance exercise, there was a significant interaction (day × group, p < 0.001). The degree of changes in MURT from DAY1-PRE to DAY8-PRE was significantly correlated with the percentage change of MUFR from DAY8-PRE to DAY8-POST in QUE (p = 0.014, r = -0.363) but not in PLA (p = 0.518). The study suggests that 7-day quercetin ingestion alters the motor unit recruitment pattern, and this may induce changes in motor unit firing patterns during a single session of resistance training (Trial registration: UMIN000052255, R000059650).

Association between expiratory mouth pressure and abdominal muscle activity in healthy young males

PURPOSE

To clarify the association between forced expiration and the abdominal muscles by assessing the relationship between expiratory mouth pressure and abdominal muscle activity in healthy young males.

METHODS

Twenty-five males underwent forced expiration at 20, 30, 50, 75, and 100% of the maximal expiratory mouth pressure. Mouth pressure was measured using a bridge-type transducer connected to a mouth pressure meter. Abdominal crunch, twist crunch, and abdominal hollowing at maximal voluntary contraction were also performed. During forced expiration and abdominal exercises, the activity of the rectus abdominis (RA), oblique externus abdominis/oblique internus abdominis (OE/OI), and OI/transversus abdominis (OI/TrA) was measured using surface electromyography.

RESULTS

The determination coefficient (r2) for the linear relationship between mouth pressure and abdominal muscle activity was 0.86 ± 0.15 for the RA, 0.93 ± 0.06 for the OE/OI, and 0.90 ± 0.14 for the OE/OI. The slope of the linear relationship with r2 ≥ 0.50 showed no significant difference between the RA (0.22 ± 0.27) and the OE/OI (0.27 ± 0.21). However, it was significantly greater in the OI/TrA (1.78 ± 1.41) than in the RA and OE/OI. The OE/OI activity was significantly lower in the maximal forced expiration than in twist crunch, and the OI/TrA activity was not significantly greater in the maximal forced expiration than in twist crunch.

CONCLUSION

All abdominal muscles contribute to forced expiration with a greater contribution of the OI and TrA than the RA and OE. Furthermore, the contribution of the TrA would be greater than that of the OI.

Acute effects of caffeine or quercetin ingestion on motor unit firing pattern before and after resistance exercise

The aim of the present study was to investigate the acute effect of caffeine or quercetin ingestion on motor unit firing patterns and muscle contractile properties before and after resistance exercise. High-density surface electromyography (HDs-EMG) during submaximal contractions and electrically elicited torque in knee extensor muscles were measured before (PRE) and 60 min after (POST1) ingestion of caffeine, quercetin glycosides, or placebo, and after resistance exercise (POST2) in ten young males. The Convolution Kernel Compensation technique was used to identify individual motor units of the vastus lateralis muscle for the recorded HDs-EMG. Ingestion of caffeine or quercetin induced significantly greater decreases in recruitment thresholds (RTs) from PRE to POST1 compared with placebo (placebo: 94.8 ± 9.7%, caffeine: 84.5 ± 16.2%, quercetin: 91.9 ± 36.7%), and there were significant negative correlations between the change in RTs (POST1-PRE) and RT at PRE for caffeine (rs = - 0.448, p < 0.001) and quercetin (rs =  - 0.415, p = 0.003), but not placebo (rs =  - 0.109, p = 0.440). Significant positive correlations between the change in firing rates (POST2-POST1) and RT at PRE were noted with placebo (rs = 0.380, p = 0.005) and quercetin (rs = 0.382, p = 0.007), but not caffeine (rs = 0.069, p = 0.606). No significant differences were observed in electrically elicited torque among the three conditions. These results suggest that caffeine or quercetin ingestion alters motor unit firing patterns after resistance exercise in different threshold-dependent manners in males.

Differences in acute neuromuscular response after single session of resistance exercise between young and older adults

AIMS

The purpose of this study was to investigate differences in the acute response after resistance exercise between young and older adults.

METHODS

Seventeen young and 18 older adults performed a single session of resistance exercise, consisting of 3 sets of 10 isometric knee extensions. Maximal voluntary contraction (MVC), motor unit (MU) activity of the vastus lateralis, and electrically elicited torque of the knee extensor were measured before and after the resistance exercise.

RESULTS

Although both groups showed the same degree of decline in MVC (young: -15.2 ± 14.3 %, older: -16.4 ± 7.9 %, p = 0.839), electrically elicited torque markedly decreased in the young group (young: -21.5 ± 7.7 %, older: -14.3 ± 9.5 %, p < 0.001), and the decrease in the MU firing rate was greater in the older group (young: -26.1 ± 24.1 %, older: -44.7 ± 24.5 %, p < 0.001). Changes in the MU firing rate following the exercise were correlated with the MU recruitment threshold in the older group (p < 0.001, rs = 0.457), but not young group (p = 0.960).

DISCUSSION

These results showed that young adults exhibited a greater acute response in the peripheral component, whereas older adults showed a greater acute response in the central component of the neuromuscular system, and the acute response in MUs with a high recruitment threshold following resistance exercise was smaller than in those with a low recruitment threshold in older adults. These findings may partly explain why there are different chronic adaptations to resistance training between young and older adults.

Effects of high-intensity inspiratory muscle warm-up on inspiratory muscle strength and accessory inspiratory muscle activity

This study aimed to determine the effects of work-matched moderate-intensity and high-intensity inspiratory muscle warm-up (IMW) on inspiratory muscle strength and accessory inspiratory muscle activity. Eleven healthy men performed three IMWs at different intensities, namely, placebo, moderate-intensity, and high-intensity, set, respectively, at 15%, 40%, and 80% of maximal inspiratory mouth pressure (MIP). MIP was measured before and after IMW. Electromyography (EMG) was recorded for the sternocleidomastoid muscle (SCM) and intercostal muscles (IC) during IMW. MIP increased significantly in the moderate-intensity condition (104.2 ± 5.1%, p<0.05) and high-intensity condition (106.5 ± 6.2%, p<0.01) after IMW. The EMG amplitudes of the SCM and IC during IMW were significantly higher in the order of high-intensity, moderate-intensity, and placebo conditions. There was a significant correlation between changes in MIP and EMG amplitude of the SCM (r=0.60, p<0.01) and IC (r=0.47, p<0.01) during IMW. These findings suggest that high-intensity IMW increases neuromuscular activity in the accessory inspiratory muscles, which may improve inspiratory muscle strength.

Effect of inspiratory resistive training on diaphragm shear modulus and accessory inspiratory muscle activation

This study aimed to elucidate changes in diaphragm and accessory inspiratory muscle (sternocleidomastoid (SCM) muscle and intercostal muscle (IC)) function after a 6-week training program. Nineteen male elite collegiate swimmers were assigned to either a control group (n = 9) or training group (n = 10). The subjects in the training group performed 30 maximum inspirations at a load resistance of 50% of maximum inspiratory mouth pressure (PImax) using an inspiratory muscle training device. These were conducted twice per day and 6 days per week. At baseline and after 6 weeks, PImax, shear modulus of the diaphragm, and electromyograms (EMG) of the SCM and IC during a maximal inspiratory maneuver were evaluated. Relative change in PImax was greater in the training group than in controls. The shear modulus during a PImax maneuver had increased significantly in both groups after 6 weeks. EMG amplitudes of the SCM increased in the training group after 6 weeks, but not in the control group. EMG amplitudes of the IC did not change after 6 weeks in either group. These results suggest that 6-week inspiratory resistive training significantly improves the activation of the SCM, which could be one of the major mechanisms behind increases in inspiratory muscle strength after resistive training. Novelty Six-week inspiratory resistive training increased diaphragm stiffness during maximal inspiration maneuver. Six-week inspiratory resistive training increased electromyogram amplitudes of the sternocleidomastoid during maximal inspiration maneuver.

Sprinting Ability as an Important Indicator of Performance in Elite Long-Distance Runners

PURPOSE

Increases in maximal oxygen uptake (V˙O2max) and running economy improve performance in long-distance runners. Nevertheless, long-distance runners require sprinting ability to win, especially in the final phase of competitions. The authors determined the relationships between performance and sprinting ability, as well as other abilities in elite long-distance runners.

METHODS

The subjects were 12 elite long-distance runners. Mean official seasonal best times in 5000-m (5000 m-SB) and 10,000-m (10,000 m-SB) races within 1 year before or after the examination were 13:58.5 (0:18.7) and 28:37.9 (0:25.2) (mean [SD]), respectively. The authors measured 100-m and 400-m sprint times as the index of sprinting ability. They also measured V˙O2max and running economy (V˙O2 at 300 m·min-1 of running velocity). They used a single correlation analysis to assess relationships between 5000 m-SB or 10,000 m-SB and other elements.

RESULTS

There were significant correlations between 5000 m-SB was significantly correlated with 100-m sprint time (13.3 [0.7] s; r = .68, P = .014), 400-m sprint time (56.6 [2.7] s; r = .69, P = .013), and running economy (55.5 [3.9] mL·kg-1·min-1; r = .59, P = .045). There were significant correlations between 10,000 m-SB and 100-m sprint time (r = .72, P = .009) and 400-m sprint time (r = .85, P < .001). However, there was no significant correlation between 5000 m-SB or 10,000 m-SB and V˙O2max (72.0 [3.8] mL·kg-1·min-1).

CONCLUSIONS

The authors' data suggest that sprinting ability is an important indicator of performance in elite long-distance runners.

Effects of Respiratory Muscle Endurance Training in Hypoxia on Running Performance

PURPOSE

We hypothesized that respiratory muscle endurance training (RMET) in hypoxia induces greater improvements in respiratory muscle endurance with attenuated respiratory muscle metaboreflex and consequent whole-body performance. We evaluated respiratory muscle endurance and cardiovascular response during hyperpnoea and whole-body running performance before and after RMET in normoxia and hypoxia.

METHODS

Twenty-one collegiate endurance runners were assigned to control (n = 7), normoxic (n = 7), and hypoxic (n = 7) groups. Before and after the 6 wk of RMET, incremental respiratory endurance test and constant exercise tests were performed. The constant exercise test was performed on a treadmill at 95% of the individual's peak oxygen uptake (V˙O2peak). The RMET was isocapnic hyperpnoea under normoxic and hypoxic conditions (30 min·d). The initial target of minute ventilation during RMET was set to 50% of the individual maximal voluntary ventilation, and the target increased progressively during the 6 wk. Target arterial oxygen saturation in the hypoxic group was set to 90% in the first 2 wk, and thereafter it was set to 80%.

RESULTS

Respiratory muscle endurance was increased after RMET in the normoxic and hypoxic groups. The time to exhaustion at 95% V˙O2peak exercise also increased after RMET in the normoxic (10.2 ± 2.4 to 11.2 ± 2.6 min) and hypoxic (11.5 ± 2.6 to 12.6 ± 3.0 min) groups, but not in the control group (9.6 ± 3.2 to 9.4 ± 4.0 min). The magnitude of these changes did not differ between the normoxic and the hypoxic groups (P = 0.84).

CONCLUSION

These results suggest that the improvement of respiratory muscle endurance and blunted respiratory muscle metaboreflex could, in part, contribute to improved endurance performance in endurance-trained athletes. However, it is also suggested that there are no additional effects when the RMET is performed in hypoxia.

Diaphragmatic shear modulus at various submaximal inspiratory mouth pressure levels

This study assessed the shear modulus of the diaphragm at various submaximal inspiratory mouth pressure levels by ultrasound shear wave elastography. In 14 healthy male subjects, diaphragmatic shear moduli were assessed at end expiration during resting breathing and at submaximal inspiratory tasks at 15, 30, 45, 60, and 75% of the maximal inspiratory mouth pressure. The shear modulus increased along with mouth pressure, and the mouth-pressure-shear-modulus relationship fit the second-order polynomial regression equation (r² = 0.99 ± 0.01; all subjects, r² ≥ 0.95) better than it did the simple linear regression equation (r² = 0.94 ± 0.05; 8/14 subjects, r² ≥ 0.95). The second regression coefficient in the second-order polynomial equation was a negative value in 10 of 14 subjects, which indicates that the second-order polynomial regression equation opened downwards. These findings suggest that the diaphragmatic shear modulus increases along with inspiratory mouth pressure, but the rate of increase slows when the pressure reaches higher levels.

Muscle Thickness and Passive Muscle Stiffness in Elite Athletes: Implications of the Effect of Long-Term Daily Training on Skeletal Muscle

To examine the effect of long-term daily training on athletes’ skeletal muscle, this study determined the relation between their muscle thickness and passive muscle stiffness, and compared the muscle thickness and muscle stiffness between athletes and non-athletes. Participants were elite Japanese athletes (278 men, 200 women) from various sports and non-athletes (35 men, 35 women). Rectus femoris (RF) muscle thickness was measured using B-mode ultrasonography and was normalized to the total body mass (muscle thickness/body mass1/3). RF passive muscle stiffness (shear modulus) was assessed by ultrasound shear-wave elastography. There was a negligibly significant correlation between muscle thickness and muscle stiffness in male athletes (p=0.003; r=−0.18) but not in female athletes (p=0.764; r=0.02). Among men, muscle thickness was significantly greater in athletes than non-athletes (p<0.001), whereas muscle stiffness was significantly less in athletes than non-athletes (p=0.020). Among women, muscle thickness was significantly greater in athletes than non-athletes (p<0.001), whereas muscle stiffness did not differ significantly between athletes and non-athletes (p=0.412). These results suggest that the effect of long-term daily training performed by athletes on muscle stiffness is more complicated than that on muscle thickness.

Hyperoxia Extends Time to Exhaustion During High-Intensity Intermittent Exercise: a Randomized, Crossover Study in Male Cyclists

BACKGROUND

Some endurance athletes exhibit exercise-induced arterial hypoxemia during high-intensity exercise. Inhalation of hyperoxic gas during exercise has been shown to counteract this exercise-associated reduction in hemoglobin oxygen saturation (S_aO₂), but the effects of hyperoxic gas inhalation on performance and S_aO₂ during high-intensity intermittent exercise remain unclear. This study investigated the effects of hyperoxic gas inhalation on performance and S_aO₂ during high-intensity intermittent cycling exercise.

METHODS

Eight male cyclists performed identical intermittent exercise tests (five sets of 3-min high-intensity cycling alternated with 3-min active recovery periods) under two different inspired air conditions, hyperoxia (HO; FIO₂ = 0.36) and normoxia (NO; FIO₂ = 0.21). The fifth set of each test was terminated at exhaustion, and the exercise time to exhaustion was recorded. Variables associated with arterial oxygen saturation (SpO₂) were measured using an ear pulse oximeter.

RESULTS

Time to exhaustion under HO conditions was significantly longer than under NO conditions (34.9 ± 4.6 vs. 30.0 ± 2.5 min, P = 0.004, ES = 1.32). SpO₂ was maintained under HO conditions but decreased under NO conditions.

CONCLUSIONS

Hyperoxic gas inhalation during the entire high-intensity intermittent exercise enhanced exercise performance in male cyclists.

Inspiratory muscle warm-up has no impact on performance or locomotor muscle oxygenation during high-intensity intermittent sprint cycling exercise

The purpose of this study was to investigate the effect of inspiratory muscle (IM) warm-up on performance and locomotor muscle oxygenation during high-intensity intermittent sprint cycling exercise. Ten subjects performed identical exercise tests (10 × 5 s with 25-s recovery on a cycle ergometer) after performing one of two different IM warm-up protocols. The IM warm-up consisted of two sets of 30 inspiratory efforts against a pressure-threshold load equivalent to 15 % (PLA) or 40 % (IMW) of maximal inspiratory pressure (MIP). MIP was measured with a portable autospirometer. Peak power and percent decrease in power were determined. Oxyhemoglobin (O₂Hb) was measured using near-infrared spectroscopy. The MIP increased relative to baseline after IMW (115 ± 21 vs. 123 ± 17 cmH₂O, P = 0.012, ES = 0.42), but not after PLA (115 ± 20 vs. 116 ± 17 cmH₂O). Peak power (PLA: 10.0 ± 0.6 vs. IMW: 10.2 ± 0.5 W kg⁻¹), percent decrease in power (PLA: 13.4 ± 5.6 vs. IMW: 13.2 ± 5.5 %), and changes in O₂Hb levels (PLA: −10.8 ± 4.8 vs. −10.7 ± 4.1 μM) did not differ between the trials. IM function was improved by IMW. However, this did not enhance performance or locomotor muscle oxygenation during high-intensity intermittent sprint cycling exercise in untrained healthy males.

Cervicofacial subcutaneous emphysema associated with dental laser treatment

Cervicofacial subcutaneous emphysema is a rare complication of dental procedures. Although most cases of emphysema occur incidentally with the use of a high-speed air turbine handpiece, there have been some reports over the past decade of cases caused by dental laser treatment. Emphysema as a complication caused by the air cooling spray of a dental laser is not well known, even though dental lasers utilize compressed air just as air turbines and syringes do. In this study, we comprehensively reviewed cases of emphysema attributed to dental laser treatment that appeared in the literature between January 2001 and September 2012, and we included three such cases referred to us. Among 13 cases identified in total, nine had cervicofacial subcutaneous and mediastinal emphysema. Compared with past reviews, the incidence of mediastinal emphysema caused by dental laser treatment was higher than emphysema caused by dental procedure without dental laser use. Eight patients underwent CO2 laser treatment and two underwent Er:YAG laser treatment. Nine patients had emphysema following laser irradiation for soft tissue incision. Dentists and oral surgeons should be cognizant of the potential risk for iatrogenic emphysema caused by the air cooling spray during dental laser treatment and ensure proper usage of lasers.

Physiological responses in Alpine skiers during on-snow training simulation in the cold

This study examined the physiological responses to cold stimulus during intermittent high-intensity exercise simulating on-snow alpine ski training. 7 male alpine skiers performed intermittent high-intensity exercises composed of 4 bouts of cycling exercise at 140% VO 2max intensity for 30 s with 10-min rests on a cycle ergometer in cold (1°C) and control (22°C) conditions. The subjects wore racing suits, middle layers and half pants designed for alpine skiers. Rectal temperature and mean skin temperature were lower in the cold condition than in the control condition (36.8 ± 0.5 vs. 37.1 ± 0.1°C and 28.4 ± 0.6 vs. 33.3 ± 0.6°C, respectively). Oxygen consumption during rests and the last 2 bouts of exercise was higher in the cold condition than in the control condition. Although plasma noradrenaline and serum triglyceride were higher in the cold condition than in the control condition, plasma glucose, adrenaline and serum glycerol were lower. Serum free fatty acid and plasma lactate concentrations did not differ significantly between the 2 conditions. These results indicate that a cold stimulus affects body temperature and energy metabolism and may lead to a decrease in exercise capacity in alpine skiers during on-snow training.

Effect of duration of active or passive recovery on performance and muscle oxygenation during intermittent sprint cycling exercise

We compared the effect of recovery condition and durations on performance and muscle oxygenation during short-duration intermittent sprint exercise. 8 subjects performed a graded test and ten 5-s maximal sprints with 25-, 50-, and 100-s passive recovery (PR) or active recovery (AR) on a cycle ergometer. Peak power and percent decrease in power were determined. Oxygen uptake and blood lactate were measured during the sprint exercise. Oxyhemoglobin (O2Hb) and deoxyhemoglobin were measured using near-infrared spectroscopy. Peak power values were higher for PR than AR for the 25-s (2-9 sprints) and 50-s (2-6, 9, or 10 sprints) but not for the 100-s durations. Percentage decrease in peak power was lower for PR than AR in the 25-s (8.5±2.5 vs. 11.5±3.6%, P=0.008, ES=0.66) and 50-s (2.7±1.4 vs. 6.2±3.5%, P=0.007, ES=0.67) but not 100-s durations (2.1±1.3 vs. 3.1±2.6%, P>0.05). O2Hb variations were significantly higher for PR than AR for the 25-s and 50-s durations. AR was associated with reduced sprint performance and lower muscular reoxygenation. Performance was not affected over longer recovery durations regardless of recovery condition.

Electrical remodeling in fibrillating canine atrium: action potential alternans during rapid atrial pacing and late phase 3 early afterdepolarization after cessation of rapid atrial pacing

Sustained atrial fibrillation (AF) was induced by atrial burst pacing, and monophasic action potentials (MAPs) were recorded. MAP alternans was observed at a cycle length (CL) of 167.5 ± 28.2 msec before burst pacing and 201.3 ± 40.2 msec after burst pacing. AF > 5 minutes duration was induced in 1 dog in the control condition but in all 8 dogs after burst pacing. The difference in RA MAPD(80) of the first spontaneous beat and steady-state sinus rhythm was significantly larger after atrial burst pacing than before atrial burst pacing (31.5 ± 15.9 msec versus 8.2 ± 9.0 msec) In 4 dogs, late phase 3 early after depolarization was observed after rapid atrial pacing. Rapid atrial pacing-induced electrical remodeling includes APD alternans during rapid atrial pacing and also causes an increase in the MAPD of the initial several beats and the development of late phase 3 early afterdepolarizations after a sudden increase in CL.