Predicting endurance limits in arm cranking exercise with a subjectively based method

CRITICAL VS ESTIMATED HEART RATE IN ELDERLY SUBJECTS

ABSTRACT Introduction: Heart rate (HR) has been a simple and easy-to-use physiological parameter widely used to determine exercise intensity. The critical power fatigue limit model, known as the critical heart rate (CHR), can be extrapolated to HR. However, an estimate for a CHR mathematical model has not yet been extrapolated for upper limb exercise in the elderly. Objective: To compare the mathematical model previously used to estimate CHR with the heart rate values at the critical power (CP) during arm-ergometer exercises in elderly subjects. Methods: After an initial maximum-incremental exercise test on a cycle arm-ergometer, seven elderly people performed four high-intensity constant-load tests to the limit of tolerance (Tlim), to determine CP and critical heart rate (CHR). For each power output, the heart rate of the last five seconds (HRlim) and total time to exhaustion (in minutes) were obtained. The slope coefficients of the regression lines between HRlim and Tlim were defined as CHR, and between Wlim and Tlim as CP. A square-wave test was performed on a different day, in the power determined as equivalent to CP, and the heart rate at CP (CPHR) was assessed. Results: The HR-Tlim relationship was found to be hyperbolic in all subjects, who were able to sustain upper-limb exercise at CP for 20 min. CP attained 66.8±9.4% of peak work rate in the ramp test. The real average HR measured in the CP test was strikingly similar to the CHR calculated by the mathematical model of PC (137.6±16.9 versus 139.7±13.3bpm, respectively, p=0.53). There was strong correlation between the real and the estimated CHR. Conclusion: This study indicated that the maximal sustainable exercise intensity can be based on a physiological variable such as HR, and the CHR test can define exercise endurance, which can be useful in performance assessment and training prescription. Level of evidence II; Diagnostic studies – Investigating a diagnostic test.

Minimal Effects of Moderate Normobaric Hypoxia on the Upper Body Work-Time Relationship in Recreationally Active Women

Background: Sex-based differences in metabolism and morphological characteristics may result in unique exercise responses during periods of limited oxygen availability. Purpose: To evaluate the effects of moderate normobaric hypoxia on the parameters of the work-time relationship during upper body exercise in women. Materials and Methods: Thirteen recreationally active women (age: 22.7 ± 2.6 years; height: 167 ± 8.6 cm; weight: 66.4 ± 9.7 kg; body fat: 27.6% ± 5% body fat) completed a maximal graded exercise test in both normobaric hypoxia (H; fraction of inspired oxygen (F_iO₂) = 0.14) and normoxia (N; F_iO₂ = 0.20) on an arm ergometer to determine peak oxygen uptake (VO₂peak) and peak power output (PPO). Each participant completed four constant, work rate, arm-cranking time-to-exhaustion tests at 90%-120% PPO in both environmental conditions. Linear regression was used to estimate critical power (CP) and anaerobic capacity (W') through the work-time relationship during the constant work rate tests. Paired sample t-tests compared mean differences between VO₂peak, PPO, CP, and W' between conditions (normoxia vs. hypoxia). Two-way (condition × intensity) repeated measures analysis of variance (ANOVA) was used to compare total work (TW) and time to exhaustion. Results: Hypoxia significantly reduced VO₂peak (N: 1.73 ± 0.31 L·minute^-1 vs. H: 1.62 ± 0.27 L·minute^-1, p = 0.008), but had no effects on PPO (N: 78.08 ± 14.51 W vs. H: 75.38 ± 13.46 W, p = 0.09), CP (N: 57.44 ± 18.89 W vs. H: 56.01 ± 12.36 W, p = 0.55), and W' (N: 4.81 ± 1.01 kJ vs. H: 4.56 ± 0.91 kJ, p = 0.51). No significant condition × intensity interactions were noted for TW or time to exhaustion (p > 0.05). Conclusions: Moderate normobaric hypoxia significantly reduced VO₂peak, but had minimal effects on CP and W' using the work-time model in women.

Critical power for the upper limb in patients with chronic obstructive pulmonary disease: A pilot study

PURPOSE

To investigated the impact of the ventilatory constraints in the power-duration relationship for upper limbs exercise in patients with chronic obstructive pulmonary disease (COPD).

METHODS

Eight patients with COPD and eight healthy subjects performed an arm incremental test on cycle ergometer and four constant workload tests (100%, 90%, 80% and 70% of peak workload). The power-duration (or critical power - CP) estimative was determined. The inspiratory capacity was measured before and after each test.

RESULTS

There was no significant difference in the CP between patients and controls. Also, the curvature constant (W_AT, work do able above CP) was similar between patients and control subjects. Finally, the limits of tolerance for all constant workload tests in the patients with COPD were closely associated with the presence of dynamic hyperinflation and ventilatory reserve.

CONCLUSION

Despite patients typically showed more ventilatory stress compared with control subjects, the ventilatory constraints did not limit the sustained upper limbs exercise at the critical power.

Characterization of the work-time relationship during cross-country ski ergometry

The purpose of this study was to examine the validity and reliability of estimated parameters of the work-time relationship during cross-country ski ergometry using the traditional multi-trial critical power (CP) test and a 3 min 'all-out' test (3MT). Fourteen recreationally active male participants (mean ± SD; age: 22.14 ± 2.85 yrs; height: 177.09 ± 6.57 cm; weight: 85.68 ± 13.56 kg) completed three testing visits. All testing was conducted using an upper-body ergometer (SkiErg, Concept2, Inc., Morrisville, VT). A graded exercise test was used to determined maximal oxygen uptake (VO2peak). Two separate 3MT sessions were used to determine oxygen uptake (VO23MT), end-test power (EP), work above end-test power (WEP) and end stroke rate (ESR). Additionally, three time trials completed in a single day at simulated distances of 300 m, 650 m and 1000 m were used to estimate CP, W' and critical stroke rate (CSR). VO2peak (3.65 ± 0.50 l · min(-1)) and VO23MT (3.59 ± 0.4 l · min(-1)) were not significantly different (p = 0.162). Intraclass correlation coefficients for EP, WEP and ESR were 0.809, 0.611 and 0.783, respectively. EP (148 ± 33 W) and CP (157 ± 49 W), were not significantly different between the testing methodologies (p = 0.290) and were highly correlated (r = 0.780). WEP (8.4 ± 3.0 kJ) and W' (8.3 ± 3.0 kJ) were similar (p = 0.947) but not related (r = 0.119), while ESR (45 ± 7 spm) and CSR (47 ± 7 spm) values were not significantly different (p = 0.238) and moderately correlated (r = 0.498). The 3MT using ski ergometry was shown to produce concurrently valid results with the traditional multi-trial CP test for CP and CSR, but not W', and elicited similar maximal oxygen uptake values when compared to a graded exercise test.

The relationship between perceived exertion and physiologic indicators of stress during graded arm exercise in persons with spinal cord injuries

OBJECTIVE

To examine the relationship between psychologic cues of somatic stress and physiologic responses to exercise in persons with paraplegia and tetraplegia.

DESIGN

Repeated measures with 2 comparison groups.

SETTING

Academic medical center.

PARTICIPANTS

Forty-two subjects between 18 and 69 years of age with motor-complete spinal cord injury (SCI) resulting in paraplegia or tetraplegia (American Spinal Injury Association grades A and B).

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Subjects underwent peak graded arm ergometry during which heart rate, oxygen consumption (VO2), minute ventilation (VE), and ratings of perceived exertion (RPE) (Borg Categorical 6-20 Scale) were measured at successive work rate increments from baseline to fatigue.

RESULTS

There were inconsistent associations among the outcomes. For subjects with tetraplegia, RPE related positively to heart rate at the initial work rate, but there were no other significant correlations. For subjects with paraplegia, RPE did not correlate significantly with heart rate, VO2, or VE. VO2 and Ve related positively at the first and last work rates. In general, heart rate, VO2, and Ve increased as the exercise intensity increased, and were more pronounced in subjects with paraplegia. While RPE values increased with increasing work rates for each group, we found no differences between groups.

CONCLUSIONS

Our findings contradict the well-accepted relationships between RPE and both heart rate and VO2 during exercise by people without disabilities, and challenge the use of RPE as a valid psychophysiologic index of perceived exertion in persons with SCI.

Muscular performance modeling of the upper limb in static postures

The purpose of the present paper is to describe and evaluate the polynomial models for predicting the muscular work capacity of the upper limb during sustained holding tasks. This research was concerned with the relationship between indicators of performance, i.e., specific posture or specific level of maximum voluntary contraction (MVC), and then modeling the functional data based on experimental results to estimate factors that may have an effect on task performance. To this end, we designed an experiment using 10 subjects in which each subject performed sustained isometric shoulder and elbow flexion endurance exercise under 27 conditions [3 shoulder angles (SA)x3 elbow angles (EA)x3 levels of %MVC]. Throughout all experiments, subjective perception of effort was assessed using the Borg scale, every 60, 30, and 10 s during the 20%, 40%, and 60% MVC tests, respectively. Proposal models were represented by three approaches: model A: estimation of endurance time (ET), with input variables such as SA, EA, and %MVC; model B: estimation of recommendation time (RT, the time during which the operator was able to maintain a position under the desired condition), with input variables such as SA, EA, %MVC, and required rate on the Borg scale; and model C: estimation of limit strength or %MVC, with input variables such as SA, EA, request limit time for work (LT), and required rate on the Borg scale. Statistical analysis indicated that the three proposal estimation models based on polynomial regression functions showed high significance (p<0.0001). The proposal models suggested and recommended the possibility of finding the best positions entailing the reduction and minimization of total muscular strain from manual material handling tasks in different work situations, with the consequent increase in work efficiency.