Measures of excess V ̇ CO2 and recovery V ̇ CO2 as indices of performance fatigability during exercise: a pilot study

Abstract Background The severity of performance fatigability and the capacity to recover from activity are profoundly influenced by skeletal muscle energetics, specifically the ability to buffer fatigue-inducing ions produced from anaerobic metabolism. Mechanisms responsible for buffering these ions result in the production of excess carbon dioxide (CO2) that can be measured as expired CO2 ( V ̇ $$\dot{\mathrm{V}}$$ CO2) during cardiopulmonary exercise testing (CPET). The primary objective of this study was to assess the feasibility of select assessment procedures for use in planning and carrying out interventional studies, which are larger interventional studies investigating the relationships between CO2 expiration, measured during and after both CPET and submaximal exercise testing, and performance fatigability. Methods Cross-sectional, pilot study design. Seven healthy subjects (30.7±5.1 years; 5 females) completed a peak CPET and constant work-rate test (CWRT) on separate days, each followed by a 10-min recovery then 10-min walk test. Oxygen consumption ( V ̇ $$\dot{\mathrm{V}}$$ O2) and V ̇ $$\dot{\mathrm{V}}$$ CO2 on- and off-kinetics (transition constant and oxidative response index), excess- V ̇ $$\dot{\mathrm{V}}$$ CO2, and performance fatigability severity scores (PFSS) were measured. Data were analyzed using regression analyses. Results All subjects that met the inclusion/exclusion criteria and consented to participate in the study completed all exercise testing sessions with no adverse events. All testing procedures were carried out successfully and outcome measures were obtained, as intended, without adverse events. Excess- V ̇ $$\dot{\mathrm{V}}$$ CO2 accounted for 61% of the variability in performance fatigability as measured by V ̇ $$\dot{\mathrm{V}}$$ O2 on-kinetic ORI (ml/s) (R 2=0.614; y = 8.474x − 4.379, 95% CI [0.748, 16.200]) and 62% of the variability as measured by PFSS (R 2=0.619; y =  − 0.096x + 1.267, 95% CI [−0.183, −0.009]). During CPET, V ̇ $$\dot{\mathrm{V}}$$ CO2 -off ORI accounted for 70% (R 2=0.695; y = 1.390x − 11.984, 95% CI [0.331, 2.449]) and V ̇ $$\dot{\mathrm{V}}$$ CO2 -off Kt for 73% of the variability in performance fatigability measured by V ̇ $$\dot{\mathrm{V}}$$ O2 on-kinetic ORI (ml/s) (R 2=0.730; y = 1.818x − 13.639, 95% CI [0.548, 3.087]). Conclusion The findings of this study suggest that utilizing V ̇ $$\dot{\mathrm{V}}$$ CO2 measures may be a viable and useful addition or alternative to V ̇ $$\dot{\mathrm{V}}$$ O2 measures, warranting further study. While the current protocol appeared to be satisfactory, for obtaining select cardiopulmonary and performance fatigability measures as intended, modifications to the current protocol to consider in subsequent, larger studies may include use of an alternate mode or measure to enable control of work rate constancy during performance fatigability testing following initial CPET

Recovery Off-Kinetics Following Exhaustive Upper Body Exercise in Spinal Cord Injury

People with spinal cord injury (SCI) present with impaired autonomic control when the lesion is above T6. This could lead to delayed cardiorespiratory recovery following vigorous physical activity. To characterize and compare gas exchange off-kinetics following exhaustive exercise in individuals with SCI and an apparently healthy control group. Participants were 19 individuals with SCI who presented with the inability to voluntarily lift their legs against gravity (age, 44.6 ± 14.2 years; AIS A, = 5; AIS B, = 7; AIS C, = 7; paraplegia, = 14; tetraplegia, = 5) and 10 healthy comparisons (COM; age, 30.5 ± 5.3 years). All participants performed an arm ergometer cardiopulmonary exercise test (aCPET) to volitional exhaustion followed by a 10-minute passive recovery. O uptake ( ) and CO output ( ) off-kinetics was examined using a mono-exponential model in which tau ( ) and mean response time (MRT) were determined. The off-kinetics transition constant ( ) was calculated as Δ /MRT. Student tests were used to compare SCI versus COM group means. COM had a significantly higher relative peak compared to SCI (1.70 ± 0.55 L/min vs 1.19 ± 0.51 L/min, = .019). No difference was observed for between the groups, however for both and was significantly lower in the SCI compared to the COM group. A reduced during recovery may suggest inefficiencies in replenishing muscle ATP stores and lactate clearance in these participants with SCI. These findings may contribute to the observed lower cardiorespiratory fitness and greater fatigability typically reported in individuals with SCI

The association of breathing pattern with exercise tolerance and perceived fatigue in women with systemic lupus erythematosus: an exploratory case-control study

The aims of the study were to (1) to characterize the breathing pattern and work of breathing during peak exercise in patients with SLE; (2) to examine the extent to which the breathing pattern and work of breathing impact the exercise capacity and fatigue. Forty-one women participated in the study (SLE: n = 23, median = 35, range = 21-57 years, control: n = 18, median = 38, range = 22-45 years). Each subject performed a treadmill cardiopulmonary exercise test (a modified Bruce treadmill protocol) ending with volitional exhaustion. Breathing mechanic was characterized by measures of expired minute volume (V), tidal volume (Vt), respiratory rate (f), work of breathing, and cardiorespiratory fitness was quantified by measures of peak oxygen consumption (VO) and time to exhaustion. Data presented as median and interquartile range (IQR). Women with SLE had lower Vt {1221 [488.8] mL/min vs. 1716 [453.1] mL; p = .006}, V {58.9 [18.9] L/min vs 70 [28.1] L/min, p = 0.04} and increased breathing frequency {51.5 [10.8] vs 43.6 [37.8] bpm, p = 0.01} compared to the control group. The time to exhaustion and peak VO during the CPET were significantly reduced in those with SLE compared to controls {13.3 [10.2] vs 16.1 [2.2] min; p = 0.004}, {20 [6.1] mL/kg/min vs 26.6 [7] mL/kg/min p \u3c 0.001}, respectively. Differences remained when the analyses were controlled for the observed differences in peak VO. When the regression model adjusted for the peak VO, it had been shown that Vt, WOB and f were explained variances in the fatigue severity by 64% [p \u3c 0.001]. The decline in V and Vt coupled with a decreased peak VO and work of breathing may have contributed to low cardiorespiratory fitness and fatigue in patients with systemic lupus erythematosus

Walking endurance, muscle oxygen extraction, and perceived fatigability after overground locomotor training in incomplete spinal cord injury: A pilot study

The purpose of this study was to examine the effects of overground locomotor training (OLT) on walking endurance and gastrocnemius oxygen extraction in people with chronic cervical motor-incomplete spinal cord injury (SCI). Prospective single-arm pre-post pilot study. Human Performance Research Laboratory. Adult men with traumatic chronic cervical SCI ( = 6; age = 30.8 ± 12.5). Twenty-four sessions of structured OLT. Walking endurance was determined during a constant work-rate time-to-exhaustion treadmill test. Normalized perceived fatigability was calculated by dividing subjective ratings of tiredness by walking time. Cardiorespiratory outcomes and muscle oxygen extraction were analyzed using breath-by-breath gas-exchange and near-infrared spectroscopy. OLT resulted in large effects on walking endurance (1232 ± 446 s vs 1645 ± 255 s;  = 1.1;  = 0.045) and normalized perceived fatigability (5.3 ± 1.5 a.u. vs 3.6 ± 0.9 a.u.;  = 1.3;  = 0.033). Small-to-medium effects on absolute (2.8 ± 2.5 a.u. vs 4.2 ± 3.5 a.u.;  = 0.42;  = 0.035) and isotime (2.8 ± 2.5 a.u. vs 3.8 ± 3.0 a.u.;  = 0.33;  = 0.023) muscle oxygen extraction were also observed after OLT. These findings provide preliminary data supporting the potential for improved walking endurance, enhanced muscle O extraction, and reduced perceived fatigability in people with chronic cervical motor-incomplete SCI following the OLT program described in this study

Oxygen uptake on-kinetics before and after aerobic exercise training in individuals with traumatic brain injury

<p><b>Objective:</b> The high prevalence of fatigue among persons with traumatic brain injury (TBI) may be related to poor cardiorespiratory fitness observed in this population. Oxygen uptake on-kinetics is a method of assessing cardiorespiratory fitness and may be used to examine performance fatigability (decline in performance during a given activity) in persons with TBI.</p> <p><b>Purpose:</b> To examine the effect of aerobic exercise training on oxygen uptake on-kinetics during treadmill walking in individuals with TBI.</p> <p><b>Methods:</b> Seven ambulatory adults with chronic non-penetrating TBI performed short moderate-intensity (3–6 metabolic equivalents) walking bouts on a treadmill, prior to and following an aerobic exercise training program (clinicaltrials.gov: NCT01294332). The 12-week training program consisted of vigorous-intensity exercise on a treadmill for 30 min, 3 times a week. Breath-by-breath pulmonary gas exchange was measured throughout the bouts, and oxygen uptake on-kinetics described the time taken to achieve a steady-state response.</p> <p><b>Results:</b> Faster oxygen uptake on-kinetics was observed after exercise training, for both the absolute and relative intensity as pre-training.</p> <p><b>Conclusions:</b> Faster oxygen uptake on-kinetics following aerobic exercise training suggests an attenuated decline in physical performance during a standardized walking bout and improved performance fatigability in these individuals with TBI.Implications for rehabilitation</p><p>Severe fatigue is a common complaint among persons with traumatic brain injury (TBI).</p><p>Oxygen uptake on-kinetics may be used as an objective physiological measure of performance fatigability in persons with TBI.</p><p>Faster oxygen uptake on-kinetics following aerobic exercise training suggests improved performance fatigability in these individuals with TBI.</p><p>Aerobic exercise training appeared beneficial for reducing performance fatigability and may be considered as part of the rehabilitative strategy for those living with TBI.</p><p></p> <p>Severe fatigue is a common complaint among persons with traumatic brain injury (TBI).</p> <p>Oxygen uptake on-kinetics may be used as an objective physiological measure of performance fatigability in persons with TBI.</p> <p>Faster oxygen uptake on-kinetics following aerobic exercise training suggests improved performance fatigability in these individuals with TBI.</p> <p>Aerobic exercise training appeared beneficial for reducing performance fatigability and may be considered as part of the rehabilitative strategy for those living with TBI.</p