Measures of excess [Formula: see text]CO2 and recovery [Formula: see text]CO2 as indices of performance fatigability during exercise: a pilot study.

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 ([Formula: see text]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 ([Formula: see text]O2) and [Formula: see text]CO2 on- and off-kinetics (transition constant and oxidative response index), excess-[Formula: see text]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-[Formula: see text]CO2 accounted for 61% of the variability in performance fatigability as measured by [Formula: see text]O2 on-kinetic ORI (ml/s) (R2=0.614; y = 8.474x - 4.379, 95% CI [0.748, 16.200]) and 62% of the variability as measured by PFSS (R2=0.619; y = - 0.096x + 1.267, 95% CI [-0.183, -0.009]). During CPET, [Formula: see text]CO2 -off ORI accounted for 70% (R2=0.695; y = 1.390x - 11.984, 95% CI [0.331, 2.449]) and [Formula: see text]CO2 -off Kt for 73% of the variability in performance fatigability measured by [Formula: see text]O2 on-kinetic ORI (ml/s) (R2=0.730; y = 1.818x - 13.639, 95% CI [0.548, 3.087]). CONCLUSION: The findings of this study suggest that utilizing [Formula: see text]CO2 measures may be a viable and useful addition or alternative to [Formula: see text]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.

Carbon Dioxide Expiration and Performance Fatigability Following Aerobic Exercise Training: A Longitudinal, Observational, Pilot Study.

Purpose: This study examined the influence of aerobic exercise training (AET) on components of carbon dioxide expiration (VCO2), cardiorespiratory function, and fatigability. Methods: Twenty healthy adults completed peak cardiopulmonary exercise (CPX) and submaximal tests before and after a vigorous, 4-week AET regimen. Each test was followed by a 10-min recovery and endurance test at 70% of peak wattage attained during CPX. Fatigability was assessed using testing durations and power output. Respiratory buffering (excess VCO2) and non-buffering (metabolic VCO2) were calculated. Data were analyzed for significance (p<0.05) using regressions and paired t-tests. Results: Significant improvements in all measures of fatigability were observed after AET. A significant increase in excess VCO2 was observed, though not in metabolic VCO2. Excess VCO2 was strongly predictive of fatigability measures. Conclusion: Significant decreases in fatigability are often observed in clinical populations such as obstructive or restrictive lung disease or pulmonary hypertension following AET, even when peak cardiorespiratory function does not appear to adapt. Decreases in fatigability appear to predict longevity with no yet identified mechanism. These results suggest that respiratory buffering and metabolic components of VCO2 may adapt independently to AET, introducing foundational plausibility for an influence of respiratory buffering adaptation to AET on fatigability status.

Effects of Performance-Based Training on Gait and Balance in Individuals With Incomplete Spinal Cord Injury.

OBJECTIVE: To determine changes in balance and gait following a task-specific, performance-based training protocol for overground locomotor training (OLT) in individuals with motor-incomplete spinal cord injury (iSCI). DESIGN: Convenience sample, prepilot and postpilot study. SETTING: Human performance research laboratory. PARTICIPANTS: Adults (N=15; 12 men and 3 women; mean age [y] ± SD, 41.5±16.9), American Spinal Injury Association Impairment Scale C or D, >6 months post-spinal cord injury. INTERVENTIONS: Two 90-minute OLT sessions per week over 12 to 15 weeks. OLT sessions were built on 3 principles of motor learning: practice variability, task specificity, and progressive overload (movement complexity, resistance, velocity, volume). Training used only voluntary movements without body-weight support, robotics, electrical stimulation, or bracing. Subjects used ambulatory assistive devices as necessary. MAIN OUTCOME MEASURES: Berg Balance Scale (BBS), Spinal Cord Injury Functional Ambulation Inventory (SCI-FAI) gait parameters, spatiotemporal measures of gait (step length, step width, percent stance, stance:swing ratio) from 7 participants who walked across a pressure-sensitive walkway. RESULTS: Fourteen participants completed the OLT protocol and 1 participant completed 15 sessions due to scheduled surgery. The BBS scores showed a mean improvement of 4.53±4.09 (P<.001). SCI-FAI scores showed a mean increase of 2.47±3.44 (P=.01). Spatiotemporal measures of gait showed no significant changes. CONCLUSION: This pilot demonstrated improvements in balance and selected gait characteristics using a task-specific, performance-based OLT for chronic iSCI.

Optimization of Movement: A Dynamical Systems Approach to Movement Systems as Emergent Phenomena.

The term "movement system" has been defined as "represent(ing) the collection of systems (cardiovascular, pulmonary, endocrine, integumentary, nervous, and musculoskeletal) that interact to move the body or its component parts."5 Although we do not dispute the advantage of defining the "movement system" as a physiological system, we contend that how the profession is identified with a monolithic "movement system" is imprudent. We contend that our scientific expertise regarding "movement optimization" should move forward by reconsidering how movement is produced (and potentially optimized) as a behavioral phenomenon in itself and abandon further attempts to promote "the movement system" with a purportedly unique and static label. We believe that reframing diagnosis is possible if there is a move away from an exclusive emphasis on classification of anatomical and physiological deviations from "normal" based on organismic constraints when such data yield, at best, an incomplete insight into functional performance that includes environmental and task constraints. The recent application of complex systems approaches to disciplines as diverse as medicine, biology, economics, and meteorology warrants thoughtful consideration of the potential benefits of incorporating similar advances in conceptualization of the central questions in physical therapy.

Rat adult stem cells (marrow stromal cells) engraft and differentiate in chick embryos without evidence of cell fusion.

Cell fusion was recently reported to account for the plasticity of adult stem cells in vivo. Adult stem cells, referred to as mesenchymal stem cells or marrow stromal cells, from rat marrow, were infused into 1.5- to 2-day-old chick embryos. After 4 days, the rat cells had expanded 1.3- to 33-fold in one-third of surviving embryos. The cells engrafted into many tissues, and no multinuclear cells were detected. The most common site of engraftment was the heart, apparently because the cells were infused just above the dorsal aorta. Some of the cells in the heart expressed cardiotin, and alpha-heavy-chain myosin. GFP(+) cells reisolated from the embryos had a rat karyotype. Therefore, the cells engrafted and partially differentiated without evidence of cell fusion.