Expiratory muscle fatigue does not regulate operating lung volumes during high-intensity exercise in healthy humans

Identifying fatigue of climbing workers using physiological data based on the XGBoost algorithm

Background

High-voltage workers often experience fatigue due to the physically demanding nature of climbing in dynamic and complex environments, which negatively impacts their motor and mental abilities. Effective monitoring is necessary to ensure safety.

Methods

This study proposed an experimental method to quantify fatigue in climbing operations. We collected subjective fatigue (using the RPE scale) and objective fatigue data, including systolic blood pressure (SBP), diastolic blood pressure (DBP), blood oxygen saturation (SpO2), vital capacity (VC), grip strength (GS), response time (RT), critical fusion frequency (CFF), and heart rate (HR) from 33 high-voltage workers before and after climbing tasks. The XGBoost algorithm was applied to establish a fatigue identification model.

Results

The analysis showed that the physiological indicators of SpO2, VC, GS, RT, and CFF can effectively evaluate fatigue in climbing operations. The XGBoost fatigue identification model, based on subjective fatigue and the five physiological indicators, achieved an average accuracy of 89.75%.

Conclusion

This study provides a basis for personalized management of fatigue in climbing operations, enabling timely detection of their fatigue states and implementation of corresponding measures to minimize the likelihood of accidents.

The effects of age on dyspnea and respiratory mechanical and neural responses to exercise in healthy men

The respiratory muscle pressure generation and inspiratory and expiratory neuromuscular recruitment patterns in younger and older men were compared during exercise, alongside descriptors of dyspnea. Healthy younger (n = 8, 28 ± 5 years) and older (n = 8, 68 ± 4 years) men completed a maximal incremental cycling test. Esophageal, gastric (Pga ) and transdiaphragmatic pressures, and electromyography (EMG) of the crural diaphragm were measured using a micro-transducer and EMG catheter. EMG of the parasternal intercostals, sternocleidomastoids, and rectus abdominis were measured using skin surface electrodes. After the exercise test, participants completed a questionnaire to evaluate descriptors of dyspnea. Pga at end-expiration, Pga expiratory tidal swings, and the gastric pressure-time product (PTPga ) at absolute and relative minute ventilation were higher (p < 0.05) for older compared to younger men. There were no differences in EMG responses between older and younger men. Younger men were more likely to report shallow breathing (p = 0.005) than older men. Our findings showed younger and older men had similar respiratory neuromuscular activation patterns and reported different dyspnea descriptors, and that older men had greater expiratory muscle pressure generation during exercise. Greater expiratory muscle pressures in older men may be due to compensatory mechanisms designed to offset increasing airway resistance due to aging. These results may have implications for exercise-induced expiratory muscle fatigue in older men.

Impact of a Breathing Intervention on Engagement of Abdominal, Thoracic, and Subclavian Musculature during Exercise, a Randomized Trial

Background: Breathing technique may influence endurance exercise performance by reducing overall breathing work and delaying respiratory muscle fatigue. We investigated whether a two-month yoga-based breathing intervention could affect breathing characteristics during exercise. Methods: Forty-six endurance runners (age = 16.6 ± 1.2 years) were randomized to either a breathing intervention or control group. The contribution of abdominal, thoracic, and subclavian musculature to respiration and ventilation parameters during three different intensities on a cycle ergometer was assessed pre- and post-intervention. Results: Post-intervention, abdominal, thoracic, and subclavian ventilatory contributions were altered at 2 W·kg⁻¹ (27:23:50 to 31:28:41), 3 W·kg⁻¹ (26:22:52 to 28:31:41), and 4 W·kg⁻¹ (24:24:52 to 27:30:43), whereas minimal changes were observed in the control group. More specifically, a significant (p < 0.05) increase in abdominal contribution was observed at rest and during low intensity work (i.e., 2 and 3 W·kg⁻¹), and a decrease in respiratory rate and increase of tidal volume were observed in the experimental group. Conclusions: These data highlight an increased reliance on more efficient abdominal and thoracic musculature, and less recruitment of subclavian musculature, in young endurance athletes during exercise following a two-month yoga-based breathing intervention. More efficient ventilatory muscular recruitment may benefit endurance performance by reducing energy demand and thus optimize energy requirements for mechanical work.

The Effect of Preexercise Expiratory Muscle Loading on Exercise Tolerance in Healthy Men

PURPOSE

Acute nonfatiguing inspiratory muscle loading transiently increases diaphragm excitability and global inspiratory muscle strength and may improve subsequent exercise performance. We investigated the effect of acute expiratory muscle loading on expiratory muscle function and exercise tolerance in healthy men.

METHODS

Ten males cycled at 90% of peak power output to the limit of tolerance (TLIM) after 1) 2 × 30 expiratory efforts against a pressure-threshold load of 40% maximal expiratory gastric pressure (PgaMAX) (EML-EX) and 2) 2 × 30 expiratory efforts against a pressure-threshold load of 10% PgaMAX (SHAM-EX). Changes in expiratory muscle function were assessed by measuring the mouth pressure (PEMAX) and PgaMAX responses to maximal expulsive efforts and magnetically evoked (1 Hz) gastric twitch pressure (Pgatw).

RESULTS

Expiratory loading at 40% of PgaMAX increased PEMAX (10% ± 5%, P = 0.001) and PgaMAX (9% ± 5%, P = 0.004). Conversely, there was no change in PEMAX (166 ± 40 vs 165 ± 35 cm H2O, P = 1.000) or PgaMAX (196 ± 38 vs 192 ± 39 cm H2O, P = 0.215) from before to after expiratory loading at 10% of PgaMAX. Exercise time was not different in EML-EX versus SHAM-EX (7.91 ± 1.96 vs 8.09 ± 1.77 min, 95% CI = -1.02 to 0.67, P = 0.651). Similarly, exercise-induced expiratory muscle fatigue was not different in EML-EX versus SHAM-EX (-28% ± 12% vs -26% ± 7% reduction in Pgatw amplitude, P = 0.280). Perceptual ratings of dyspnea and leg discomfort were not different during EML-EX versus SHAM-EX.

CONCLUSION

Acute expiratory muscle loading enhances expiratory muscle function but does not improve subsequent severe-intensity exercise tolerance in healthy men.

Functional training of the inspiratory muscles improves load carriage performance

Inspiratory Muscle Training (IMT) whilst adopting body positions that mimic exercise (functional IMT; IMT_F) improves running performance above traditional IMT methods in unloaded exercise. We investigated the effect of IMT_F during load carriage tasks. Seventeen males completed 60 min walking at 6.5 km·h^-1 followed by a 2.4 km load carriage time-trial (LC_TT) whilst wearing a 25 kg backpack. Trials were completed at baseline; post 4 weeks IMT (consisting of 30 breaths twice daily at 50% of maximum inspiratory pressure) and again following either 4 weeks IMT_F (comprising four inspiratory loaded core exercises) or maintenance IMT (IMT_CON). Baseline LC_TT was 15.93 ± 2.30 min and was reduced to 14.73 ± 2.40 min (mean reduction 1.19 ± 0.83 min, p < 0.01) after IMT. Following phase two, LC_TT increased in IMT_F only (13.59 ± 2.33 min, p < 0.05) and was unchanged in post-IMT_CON. Performance was increased following IMT_F, providing an additional ergogenic effect beyond IMT alone. Practitioner Summary: We confirmed the ergogenic benefit of Inspiratory Muscle Training (IMT) upon load carriage performance. Furthermore, we demonstrate that functional IMT methods provide a greater performance benefit during exercise with thoracic loads. Abbreviations: [Lac^-]_B: blood lactate; FEV₁: forced expiratory volume in one second; FEV₁/FVC: forced expiratory volume in one second/forced vital capacity ratio; FVC: forced vital capacity; HR: heart rate; IMT: inspiratory muscle training; IMT_CON: inspiratory muscle training maintenance; IMT_F: functional inspiratory muscle training; LC: load carriage; LC_TT: load carriage time trial; P_di: transdiaphragmatic pressure; PEF: peak expiratory flow; P_Emax: maximum expiratory mouth pressure; P_Imax: maximum inspiratory mouth pressure; RPE: rating of perceived exertion; RPE_breating: rating of perceived exertion for the breathing; RPE_leg: rating of perceived exertion for the legs; SEPT: sport-specific endurance plank test; V̇ O₂: oxygen consumption; V̇ O_2peak: peak oxygen consumption.

Expiratory flow limitation under moderate hypobaric hypoxia does not influence ventilatory responses during incremental running in endurance runners

We tested whether expiratory flow limitation (EFL) occurs in endurance athletes in a moderately hypobaric hypoxic environment equivalent to 2500 m above sea level and, if so, whether EFL inhibits peak ventilation ( V ˙ Epeak ), thereby exacerbating the hypoxia-induced reduction in peak oxygen uptake ( V ˙ O2peak ). Seventeen young male endurance runners performed incremental exhaustive running on separate days under hypobaric hypoxic (560 mmHg) and normobaric normoxic (760 mmHg) conditions. Oxygen uptake ( V ˙ O2 ), minute ventilation ( V ˙ E), arterial O2 saturation (SpO2 ), and operating lung volume were measured throughout the incremental exercise. Among the runners tested, 35% exhibited EFL (EFL group, n = 6) in the hypobaric hypoxic condition, whereas the rest did not (Non-EFL group, n = 11). There were no differences between the EFL and Non-EFL groups for V ˙ Epeak and V ˙ O2peak under either condition. Percent changes in V ˙ Epeak (4 ± 4 vs. 2 ± 4%) and V ˙ O2peak (-18 ± 6 vs. -16 ± 6%) from normobaric normoxia to hypobaric hypoxia also did not differ between the EFL and Non-EFL groups (all P > 0.05). No differences in maximal running velocity, SpO2 , or operating lung volume were detected between the two groups under either condition. These results suggest that under the moderate hypobaric hypoxia (2500 m above sea level) frequently used for high-attitude training, ~35% of endurance athletes may exhibit EFL, but their ventilatory and metabolic responses during maximal exercise are similar to those who do not exhibit EFL.

Influence of Upper-Body Exercise on the Fatigability of Human Respiratory Muscles

Purpose

Diaphragm and abdominal muscles are susceptible to contractile fatigue in response to high-intensity, whole-body exercise. This study assessed whether the ventilatory and mechanical loads imposed by high-intensity, upper-body exercise would be sufficient to elicit respiratory muscle fatigue.

Methods

Seven healthy men (mean ± SD; age = 24 ± 4 yr, peak O₂ uptake [V˙O_2peak] = 31.9 ± 5.3 mL·kg⁻¹·min⁻¹) performed asynchronous arm-crank exercise to exhaustion at work rates equivalent to 30% (heavy) and 60% (severe) of the difference between gas exchange threshold and V˙O_2peak. Contractile fatigue of the diaphragm and abdominal muscles was assessed by measuring pre- to postexercise changes in potentiated transdiaphragmatic and gastric twitch pressures (P_di,tw and P_ga,tw) evoked by supramaximal magnetic stimulation of the cervical and thoracic nerves, respectively.

Results

Exercise time was 24.5 ± 5.8 min for heavy exercise and 9.8 ± 1.8 min for severe exercise. Ventilation over the final minute of heavy exercise was 73 ± 20 L·min⁻¹ (39% ± 11% maximum voluntary ventilation) and 99 ± 19 L·min⁻¹ (53% ± 11% maximum voluntary ventilation) for severe exercise. Mean P_di,tw did not differ pre- to postexercise at either intensity (P > 0.05). Immediately (5–15 min) after severe exercise, mean P_ga,tw was significantly lower than pre-exercise values (41 ± 13 vs 53 ± 15 cm H₂O, P < 0.05), with the difference no longer significant after 25–35 min. Abdominal muscle fatigue (defined as ≥15% reduction in P_ga,tw) occurred in 1/7 subjects after heavy exercise and 5/7 subjects after severe exercise.

Conclusions

High-intensity, upper-body exercise elicits significant abdominal, but not diaphragm, muscle fatigue in healthy men. The increased magnitude and prevalence of fatigue during severe-intensity exercise is likely due to additional (nonrespiratory) loading of the thorax.

Effect of abdominal binding on respiratory mechanics during exercise in athletes with cervical spinal cord injury

We asked whether elastic binding of the abdomen influences respiratory mechanics during wheelchair propulsion in athletes with cervical spinal cord injury (SCI). Eight Paralympic wheelchair rugby players with motor-complete SCI (C5-C7) performed submaximal and maximal incremental exercise tests on a treadmill, both with and without abdominal binding. Measurements included pulmonary function, pressure-derived indices of respiratory mechanics, operating lung volumes, tidal flow-volume data, gas exchange, blood lactate, and symptoms. Residual volume and functional residual capacity were reduced with binding (77 ± 18 and 81 ± 11% of unbound, P < 0.05), vital capacity was increased (114 ± 9%, P < 0.05), whereas total lung capacity was relatively well preserved (99 ± 5%). During exercise, binding introduced a passive increase in transdiaphragmatic pressure, due primarily to an increase in gastric pressure. Active pressures during inspiration were similar across conditions. A sudden, sustained rise in operating lung volumes was evident in the unbound condition, and these volumes were shifted downward with binding. Expiratory flow limitation did not occur in any subject and there was substantial reserve to increase flow and volume in both conditions. V̇o2 was elevated with binding during the final stages of exercise (8-12%, P < 0.05), whereas blood lactate concentration was reduced (16-19%, P < 0.05). V̇o2/heart rate slopes were less steep with binding (62 ± 35 vs. 47 ± 24 ml/beat, P < 0.05). Ventilation, symptoms, and work rates were similar across conditions. The results suggest that abdominal binding shifts tidal breathing to lower lung volumes without influencing flow limitation, symptoms, or exercise tolerance. Changes in respiratory mechanics with binding may benefit O2 transport capacity by an improvement in central circulatory function.