ABSTRACT 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.

Purpose. - Current practices for estimating exercise economy using an extrapolation of sub-gas exchange threshold (GET), and to a lesser degree supra-GET, data will likely result an underestimation of actual economy, however, this is yet to be empirically demonstrated. Despite contentions, these protocols remain in widespread use. Therefore, the aim of the present study was to investigate whether estimation of exercise economy from moderate only, and moderate and heavy intensity exercise underestimates actual oxygen cost. Summary of Facts and Results. - Twelve recreationally active males (mean +/- SD; age 29 +/- 9y, height 1.81 +/- 0.07 m, mass 81.4 +/- 10 kg) volunteered for this study. Following a maximal ramp test to determine the V<(O)over dot>(2peak), peak power (W-peak), V (O) triple over dot (2) and power output at GET, participants completed a sub-GET only, a sub/supra-GET (both five-stage incremental tests), and a fixed WR protocol (10 min duration at 75% Delta). Economy was determined by extrapolation of sub- and sub/supra-GET V (O) triple over dot (2) and directly measured V (O) triple over dot (2) at 75% Delta. Within-subjects ANOVA was performed to identify differences in economy between sub-GET only, sub/supra-GET, and fixed WR protocols. Significant effects between the predicted values compared to the measured value were investigated post hoc using Bonferroni corrected paired t-tests. There was a significant effect of protocol on V (O) triple over dot (2) and economy (P < 0.001, eta(2)(p) = 0.645), where both methods of estimation underestimated the actual oxygen cost. In addition, estimation-using sub-GET data was significantly lower than sub/supra-GET (P < 0.05). Conclusion. - The large error obtained by extrapolating sub-GET exercise intensities for the purpose of estimating exercise economy needs to be acknowledged, as does the concomitant, albeit reduced, error that remains when incorporating supra-GET data. Exercise scientists and practitioners should adopt more appropriate testing protocols such as serial assessments, up-to and including race pace, to accurately assess economy. (C) 2019 Elsevier Masson SAS. All rights reserved.

An exercise challenge test (ECT) that follows American Thoracic Society (ATS) guidelines is the criterion that surrogate tests for exercise-induced bronchoconstriction (EIB) should be compared (Stickland, M. et al. Annals of Allergy, Asthma & Immunology 2011; 107:229-234). Studies that have compared eucapnic voluntary hyperventilation (EVH) with ECT often fail to follow ATS guidelines. The aim of this study was to compare the airway response to EVH with the response elicited by an ECT that complied with ATS guidelines. Seventeen participants completed an ECT and an EVH test on separate days. Forced vital capacity (FVC), forced expiratory volume in 1 second (FEV1), FEV1/FVC, and peak expiratory flow (PEF) were compared to baseline to determine the response to each challenge. Bland & Altman plot analysis was used to evaluate the bias between the mean differences for ΔFEV1, and to estimate a limit of agreement (LoA) within which 95% of the differences fell. The bias was 2.2% (95% CI -0.8-5.0%) indicating that ECT tended to give a ΔFEV1 between 0.8% lower and 5% higher than EVH. The upper and lower LoA (13.7 and -9.3%, respectively) were large indicating that the ECT may result in a ΔFEV1­ between 13.7% higher and 9.3% lower than EVH. Further, the confidence intervals for the upper and lower LoA (8.5 to 18.6% and -14.5 to -4.4%, respectively) were wide, also indicating poor agreement. These data do not support the use of EVH as a suitable alternative to ECT for the detection of EIB. More data is needed to fully evaluate the utility of EVH as an airway challenge.

The purpose of this study was to determine muscle tissue oxidative capacity and recovery in intermediate, advanced, and elite rock climbers. Forty-four male participants performed (a) sustained and (b) intermittent contractions at 40% of maximal volitional contraction (MVC) on a sport-specific fingerboard until volitional fatigue. Near-infrared spectroscopy was used to assess muscle tissue oxygenation during both the exercise and the 5-minutes passive recovery period, in the flexor digitorum profundus (FDP) and flexor carpi radialis (FCR). During the sustained contraction only, muscle tissue deoxygenation (O-2 debt) in the FDP and FCR was significantly greater in elite climbers compared with the control, intermediate, and advanced groups (FDP: 32 vs. 15, 19, 22%; FCR: 19 vs. 11, 8, 15%, respectively). However, elite climbers had a significantly quicker time to half recovery (T-1/2) than the control and intermediate groups in the FDP (8 vs. 95 and 47 seconds, respectively) and the FCR (7 vs. 30 and 97 seconds, respectively) because the O-2% recovered per second being significantly greater (FDP: 4.2 vs. 0.7 and 0.3; FCR: 4.8 vs. 0.1 and 0.2, respectively). Furthermore, during the intermittent contraction, T-1/2 in elite climbers was significantly quicker compared with the control and intermediate groups in the FDP (8 vs. 93 and 83 seconds, respectively) and FCR (16 vs. 76 and 50 seconds, respectively). Consequently, lower-level climbers should focus training on specific intermittent fatigue protocols. Competition or elite climbers should make use of appropriate rests on route to aid recovery and increase the chances of reaching the next hold.

The impact of inspiratory threshold loading on constant load exercise has been examined using absolute exercise intensities (Carra, J. et al. Journal of Applied Physiology. 2003; 94: 2448-2455). However, breathing load may alter the work-rates at which VO2peak and gas exchange threshold (GET) occur. Therefore, the aim of this study was to determine the effect of threshold loading on the response to ramp exercise. Twelve active males took part in this study. At separate visits (>48 hrs.) subjects performed maximal ramp cycle tests to determine VO2peak and GET with either no inspiratory resistance or threshold loads of 15 and 30 cmH2O. Breath-by-breath V O2 data was modelled using a bi-exponential function. The effect of inspiratory load on the VO2 response to ramp exercise was determined with one way analysis of variance and post-hoc linear trend analysis. During ramp exercise there were significant linear trends in GET (P=0.041) and peak power (P=0.002). There was no effect on VO2peak (P=0.719). This study has shown that the work-rate at GET decreases as threshold-load increases. Therefore, studies investigating constant load exercise should consider the use of intensities relative to GET.

Background: Professional cyclists have been shown to have a mechanical efficiency that is 11% higher compared to amateur cyclists (Coyle et al. 1991: Med Sci Sports Exerc, 23 (1), 93-107). The variations in power between professional and amateur cyclists are associated with a greater torque development at the first phase of the pedal revolution (Coyle et al. 1991). It has also been shown in cyclists that a relationship exists between vertical leg stiffness and the peak power output (PPO) (r = 0.75, p < 0.01) achieved during a 30 s Wingate test (Pitchers et al. 2013: The relationship of vertical leg stiffness, peak power output and VI‡O2max in recreationally active cyclists: identification of the interface between human and bike. 9th Annual Conference of the United Kingdom Strength & Conditioning Association, Nottingham, UK). Vertical leg stiffness may be important to cycling performance as the majority of the force produced is vertical and optimisation of the stretch shortening cycle may limit energy wastage during the propulsive phase (So et al. 2005: Phys Ther Sports, 6, 89-96; Fonda & Sarabon 2010: Sport Sci Rev, 19 (1), 187-210). The relationship between vertical leg stiffness and mechanical efficiency during cycling has yet to be examined.  Purpose: To assess the relationship between vertical leg stiffness and gross mechanical efficiency (GE) in cycling.  Methods: In a single group, within subjects design, 11 recreationally active male cyclists (age 34 ± 6 y, VI‡O2max 57.4 ± 7.5 ml∙kg∙min-1, body mass 81 ± 1.2 kg, stature 1.81 ± 0.06 m) completed two testing sessions, with a minimum of 48 hr rest between each session. In the first testing session participants completed a stiffness familiarisation before an incremental cycle test to establish VI‡O2max. At the second session participants completed 20 sub-maximal bilateral hops at a frequency of 2.3 Hz. This was followed by three 8 min sub-maximal cycling bouts at 50, 55 and 60 % of the participants’ individual maximal minute power (MMP) to establish GE (Table I).   Results: Mean values for GE and vertical leg stiffness were 19.0 ± 1.4 % and 34.1 ± 9.0 kN∙m-1, respectively. Pearson’s correlation coefficient revealed no relationship between vertical leg stiffness and GE (r = -0.07, p = 0.85).  Discussion: The main finding is that in recreationally active male cyclists there is no relationship between vertical leg stiffness and GE. In this group these findings indicate that GE is likely influenced more by other biological systems rather than the mechanical properties of the musculoskeletal system. However, these data may not be reflective of an elite sample where higher leg stiffness might be more likely to influence GE at higher power outputs. Conclusion: Whilst vertical leg stiffness has been shown to have a strong relationship with PPO (Pitchers et al 2013) in recreational cyclists, this is not the case for GE. Further work is needed to establish if this is also the case in an elite population.

To determine whether expiratory muscle fatigue (EMF) is involved in regulating operating lung volumes during exercise, nine recreationally active subjects cycled at 90% of peak work rate to the limit of tolerance with prior induction of EMF (EMF-ex) and for a time equal to that achieved in EMF-ex without prior induction of EMF (ISO-ex). EMF was assessed by measuring changes in magnetically evoked gastric twitch pressure. Changes in end-expiratory and end-inspiratory lung volume (EELV and EILV) and the degree of expiratory flow limitation (EFL) were quantified using maximal expiratory flow-volume curves and inspiratory capacity maneuvers. Resistive breathing reduced gastric twitch pressure (-24 ± 14%, P = 0.004). During EMF-ex, EELV decreased from rest to the 3rd min of exercise [39 ± 8 vs. 27 ± 7% of forced vital capacity (FVC), P = 0.001] before increasing toward baseline (34 ± 8% of FVC end exercise, P = 0.073 vs. rest). EILV increased from rest to the 3rd min of exercise (54 ± 8 vs. 84 ± 9% of FVC, P = 0.006) and remained elevated to end exercise (88 ± 9% of FVC). Neither EELV (P = 0.18) nor EILV (P = 0.26) was different at any time point during EMF-ex vs. ISO-ex. Four subjects became expiratory flow limited during the final minute of EMF-ex and ISO-ex; the degree of EFL was not different between trials (37 ± 18 vs. 35 ± 16% of tidal volume, P = 0.38). At end exercise in both trials, EELV was greater in subjects without vs. subjects with EFL. These findings suggest that 1) contractile fatigue of the expiratory muscles in healthy humans does not regulate operating lung volumes during high-intensity sustained cycle exercise; and 2) factors other than "frank" EFL cause the terminal increase in EELV.

The severity of diaphragm fatigue is greater after exhaustive whole-body exercise compared to maximal voluntary isocapnic hyperpnea (VIH) during which diaphragm pressure is in excess of that generated during exercise; whether this occurs in the expiratory muscles is unknown. PURPOSE: To compare the severity of expiratory muscle fatigue in response to high-intensity whole-body exercise and VIH. METHODS: Five healthy male subjects participated in the study [mean ± SD peak oxygen uptake (V˙O2peak) = 47.6 ± 2.3 ml·kg-1·min-1]. On separate occasions, the subjects cycled at >90% V˙O2peak to the limit of tolerance (11.4 ± 2.1 min) and performed 2 min of VIH. Expiratory muscle fatigue was assessed following both conditions by measuring the reduction from baseline of the magnetically evoked gastric pressure (Pga) response to stimuli at 1, 5, 10, 15, 20 and 25 Hz. RESULTS: At all frequencies of stimulation, Pga was lower than baseline immediately after whole-body exercise and VIH [−25 ± 6% and −17 ± 4%, respectively (mean for all frequencies); P < 0.01]. The severity of expiratory muscle fatigue was greater after exercise versus VIH (P = 0.041). Maximum ventilation during exercise (153 ± 23 l·min-1) was lower (P < 0.05) than ventilation during the first and the last 10 s of VIH (198 ± 22 and 156 ± 15 l·min-1, respectively). The product of the tidal integral of gastric pressure and breathing frequency (∫Pga × ƒR) was lower (P < 0.01) during the first and last 10 breaths of exercise (452 ± 104 and 525 ± 96 cmH2O·s·min-1) compared to the first and last 10 breaths of VIH (1724 ± 719 and 822 ± 337 cmH2O·s·min-1). The cumulative ∫Pga, however, was not different for exercise vs. VIH (6505 ± 982 vs. 8124 ± 1051 cmH2O·s-1, P = 0.14). CONCLUSION: Although the cumulative pressure output of the expiratory muscles was similar between trials, high-intensity whole-body exercise elicited a greater degree of expiratory muscle fatigue compared with 2 min of VIH. We postulate that a greater competition for blood flow between different vascular beds during exercise compared to VIH may have accounted for the additional expiratory muscle fatigue after exercise.

Large inspiratory pressures may impart stretch to airway smooth muscle and modify the response to deep inspiration (DI) in asthmatics. Respiratory system resistance (Rrs) was assessed in response to 5 inspiratory manoeuvres using the forced oscillation technique: (a) single unloaded DI; (b) single DI at 25 cmH(2)O; (c) single DI at 50% maximum inspiratory mouth pressure [MIP]; (d) 30 DIs at 50% MIP; and (e) 30 DIs at 50% MIP with maintenance of normocapnia. Rrs increased after the unloaded DI and the DI at 25 cmH(2)O but not after a DI at 50% MIP (3.6+/-1.6 hPa Ls(-1) vs. 3.6+/-1.5 hPa Ls(-1); p=0.95), 30 DIs at 50% MIP (3.9+/-1.5 hPa Ls(-1) vs. 4.2+/-2.0 hPa Ls(-1); p=0.16) or 30 DIs at 50% MIP under normocapnic conditions (3.9+/-1.5 hPa Ls(-1) vs. 3.9+/-1.5 hPa Ls(-1); p=0.55). Increases in Rrs in response to DI were attenuated after single and multiple loaded breaths at 50% MIP.

We assessed upper airway responses to acute and chronic inspiratory loading. In Experiment I, 11 healthy subjects underwent T2-weighted magnetic resonance imaging (MRI) of upper airway dilator muscles (genioglossus and geniohyoid) before and up to 10 min after a single bout of pressure threshold inspiratory muscle training (IMT) at 60% maximal inspiratory mouth pressure (MIP). T2 values for genioglossus and geniohyoid were increased versus control (p < 0.001), suggesting that these airway dilator muscles are activated in response to acute IMT. In Experiment II, nine subjects underwent 2D-Flash sequence MRI of the upper airway during quiet breathing and while performing single inspirations against resistive loads (10%, 30% and 50% MIP); this procedure was repeated after 6 weeks of IMT. Lateral narrowing of the upper airway occurred at all loads, whilst anteroposterior narrowing occurred at the level of the laryngopharynx at loads ≥30% MIP. Changes in upper airway morphology and narrowing after IMT were undetectable using MRI.

The diaphragm fatigues in response to sustained whole-body exercise, as shown using phrenic nerve stimulation. The expiratory muscles have been shown to fatigue in response to voluntary isocapnic hyperpnea using direct nerve stimulation techniques. Whether whole-body exercise elicits expiratory muscle fatigue, as assessed using nerve stimulation, is unknown. PURPOSE: To investigate whether the expiratory muscles fatigue in response to high-intensity, whole-body exercise. METHODS: Eleven male subjects (mean ± S.E.M. peak oxygen uptake [V.O2peak] = 50.0 ± 1.9 ml kg−1 min−1, range 44.6 – 62.6) cycled at >90% V.O2peakto exhaustion (14.2 ± 4.2 min). Expiratory muscle function was assessed before and up to 30 min after exercise by magnetically stimulating the nerve roots supplying the expiratory muscles at 1 through 25 Hz and measuring the change in gastric pressure (Pga). Oneway repeated measures ANOVA was used to detect changes in expiratory muscle function after exercise. RESULTS: Immediately after exercise there was a decrease in Pga at all stimulation frequencies (mean −25 ± 4%; P <0.001) that persisted up to at least 30 min post-exercise (−12 ± 4%; P = 0.011). Concurrent declines in the Pga response to maximal voluntary expiratory efforts also occurred after exercise (158 ± 13 before vs. 145 ± 10 cmH2O after exercise, P = 0.005). The reductions in stimulated Pga were unlikely due to changes in membrane excitability because amplitude, duration and area of the rectus abdominis M-wave were unaffected. The reductions in voluntary Pga were not mediated centrally because voluntary activation, assessed using twitch interpolation, did not change (67 ± 6 before vs. 64 ± 2% after exercise, P = 0.20) and electromyographic activity of the rectus abdominis increased during the volitional maneuvers. CONCLUSIONS: Expiratory muscle fatigue is present after sustained, high-intensity exercise in normal subjects, and this fatigue is primarily due to peripheral mechanisms.

The abdominal muscles have been shown to fatigue in response to voluntary isocapnic hyperpnea using direct nerve stimulation techniques. We investigated whether the abdominal muscles fatigue in response to dynamic lower limb exercise using such techniques. Eleven male subjects [peak oxygen uptake (VO2 peak) = 50.0 +/- 1.9 (SE) ml.kg(-1).min(-1)] cycled at >90% VO2 peak to exhaustion (14.2 +/- 4.2 min). Abdominal muscle function was assessed before and up to 30 min after exercise by measuring the changes in gastric pressure (Pga) after the nerve roots supplying the abdominal muscles were magnetically stimulated at 1-25 Hz. Immediately after exercise there was a decrease in Pga at all stimulation frequencies (mean -25 +/- 4%; P < 0.001) that persisted up to 30 min postexercise (-12 +/- 4%; P = 0.001). These reductions were unlikely due to changes in membrane excitability because amplitude, duration, and area of the rectus abdominis M wave were unaffected. Declines in the Pga response to maximal voluntary expiratory efforts occurred after exercise (158 +/- 13 before vs. 145 +/- 10 cmH2O after exercise; P = 0.005). Voluntary activation, assessed using twitch interpolation, did not change (67 +/- 6 before vs. 64 +/- 2% after exercise; P = 0.20), and electromyographic activity of the rectus abdominis and external oblique increased during these volitional maneuvers. These data provide new evidence that the abdominal muscles fatigue after sustained, high-intensity exercise and that the fatigue is primarily due to peripheral mechanisms.