Oxygenation trends in vastus lateralis muscle during incremental and intense anaerobic cycle exercise in young men and women

The purposes of this study were to compare the acute cardiorespiratory responses and muscle oxygenation trends during incremental cycle exercise to exhaustion with those observed during 30 s and 45 s Wingate tests in healthy men and women, and to examine the relationships between selected variables among these tests. Seventeen healthy junior badminton players, nine men [mean age, height, body mass and maximal oxygen uptake (VO2max) were 15.8 (SD 0.8) years, 1.73 (SD 0.08) m, 65.6 (SD 6.3) kg and 50.6 (SD 6.9) ml x kg(-1) x min(-1) respectively] and eight women [mean age, height, body mass and VO2max were 16.6 (SD 1.0) years, 1.65 (SD 0.03) m, 62.7 (SD 4.5) kg and 42.0 (SD 5.0) ml x kg(-1) x min(-1) respectively] completed a stepwise incremental exercise test to voluntary exhaustion and two Wingate tests lasting 30 s and 45 s in three separate sessions in random order. Cardiorespiratory responses were monitored breath-by-breath using a metabolic cart interfaced with an electrocardiogram. Tissue absorbancy trends were continuously recorded from the right vastus lateralis muscle using dual wavelength near infrared spectroscopy. Oxygen uptake and heart rate were significantly higher during the incremental test when compared to the two Wingate tests in the men and women. However, the oxygen pulse (oxygen utilization per heart beat, i.e., the product of stroke volume and arterio-venous oxygen difference) was not significantly different among the three tests in both sexes. The minimal tissue absorbancy, an index of muscle deoxygenation, was also not significantly different among the three tests in both sexes. Significant relationships were observed for the oxygen uptake (r2=0.72) and oxygen pulse (r2=0.60) between the incremental and 45 s Wingate tests in the sample for both sexes combined. The minimal tissue absorbancy, however, was not significantly related between the two tests. It was concluded that the significantly higher oxygen uptake during the incremental test was due to the higher heart rate because: firstly, oxygen pulse was not significantly different among the three tests, and secondly, peripheral factors, as indicated by the changes in muscle oxygenation, were not significantly different among the three test conditions. Although the peak values of the oxygen pulse during the incremental and 45 s Wingate tests were significantly correlated, the common variance of the minimal tissue absorbancy measurements between these two tests was quite low, suggesting considerable variation in the peripheral contribution during these two tests.

Validity of the baltimore therapeutic equipment work simulator in the measurement of lifting endurance in healthy men

OBJECTIVE

To examine the criterion validity of the Baltimore Therapeutic Equipment (BTE) work simulator by comparing endurance time, oxygen uptake (VO2), and heart rate measured during real and simulated lifting tasks and to derive a regression equation for predicting actual lifting endurance from measurements on the work simulator.

METHOD

Twenty healthy male volunteers repetitively lifted and lowered a load of 40 lb using the BTE work simulator and actual weights at a laboratory workstation. Postures, location, and frequency of lifts were kept constant. Endurance (defined as the time taken for the rating of perceived exertion to increase 2 units on the Borg scale) was measured under both conditions. VO2 and heart rate were also recorded, using standard physiological procedures.

RESULTS

The mean values for endurance time, steady-state VO2, and heart rate were significantly different between the real and simulated tasks (p < .05). Correlation of endurance time between the two tasks was significant (r = .71, p < .05). Step wise regression analysis resulted in the following equation for predicting real endurance from simulated time measurements: predicted real time = .34 simulated time + 3.29; r = .71; SE = 1.00 min.

CONCLUSION

The BTE work simulator tends to overestimate real lifting endurance performance in healthy men. The lower physiological stress during the simulated task suggests a significant difference between the real and simulated loads. Occupational therapists should exercise caution when using the results of the BTE work simulator during functional capacity evaluations.

Quadriceps muscle deoxygenation during functional electrical stimulation in adults with spinal cord injury

STUDY DESIGN

Cross-sectional study comparing healthy subjects with age and gender matched subjects with spinal cord injury (SCI, injury levels from C5 to T12).

OBJECTIVES

To compare the acute cardiorespiratory responses and muscle oxygenation trends during functional electrical stimulation (FES) cycle exercise and recovery in the SCI and healthy subjects exercising on a mechanical cycle ergometer.

SETTING

Seven volunteers in each group participated in one exercise test at the Rick Hansen Center, University of Alberta, Edmonton, Canada.

METHODS

Both groups completed a stagewise incremental test to voluntary fatigue followed by 2 min each of active and passive recovery. Cardiorespiratory responses were continuously monitored using an automated metabolic cart and a wireless heart rate monitor. Tissue absorbency, an index of muscle oxygenation, was monitored non-invasively from the vastus lateralis using near infrared spectroscopy.

RESULTS

The healthy subjects showed significant (P<0.05) increases in the oxygen uptake (VO2), heart rate (HR) and ventilation rate (VE) from rest to maximal exercise. The SCI subjects showed a twofold increase in VO2 (P>0.05), a threefold increase in VE (P<0.05) and a 5 beats/min increase in HR (P>0.05) from the resting value. The SCI subjects demonstrated a lesser degree (P<0.05) of muscle deoxygenation than the healthy subjects during the transition from rest to exercise. Regression analysis indicated that the rate of decline in muscle deoxygenation with respect to the VO2 was significantly (P<0.05) faster in the SCI subjects compared to healthy subjects.

CONCLUSIONS

FES exercise in SCI subjects elicits: (a) modest increases in the cardiorespiratory responses when compared to resting levels; (b) lower degree of muscle deoxygenation during maximal exercise, and (c) faster changes in muscle deoxygenation with respect to the VO2 during exercise when compared to healthy subjects.

Gender differences during treadmill walking with graded loads: biomechanical and physiological comparisons

In this study, we compared the biomechanical and physiological responses of healthy men and women during bilateral load carriage while they walked on a treadmill at their self-selected velocity. Eleven men mean (SD) maximal oxygen uptake, [VO(2)(max) = 56.0 (7.1) ml x kg(-1) x min(-1)] and 11 women [VO(2)(max) = 44.6 (7.6) ml x kg(-1) x min(-1)] carried 15-kg and 20-kg loads in random order using a custom-designed load-carriage device. The load supported by each hand was measured by placing strain gauges in each handle of the device. The load supported by the body was calculated as the difference between the load carried and that supported by each hand. Physiological measurements were recorded using standard procedures, and cardiac output was measured by carbon dioxide rebreathing while standing, walking, and during load carriage. Three-way analysis of variance (gender by load by test phase) indicated no significant (P > 0.05) three-way interaction, implying that the overall trend in these responses was similar in men and women. A-priori Scheffe multiple comparisons revealed the following significant (P < 0.05) gender differences during load carriage: (1) women supported a lower proportion of the load with the hands and transferred a greater amount to the body by resting the load against the chest, (2) the oxygen uptake increased by a greater amount in the women compared with men and exceeded the ventilatory threshold during the 20-kg walk in women, and (3) the cardiovascular stress, as indicated by the percentage of maximal heart rate and rate pressure product (product of heart rate and systolic blood pressure), was significantly higher in women compared with men during both of the load-carriage walks. These observations suggest that when carrying absolute loads of 15 kg and 20 kg, women are more susceptible to fatigue and are at a greater risk of cardiovascular complications than men.

Validity and reliability of the 6 minute walk in persons with fibromyalgia

OBJECTIVE

To assess the reliability and construct validity of the 6 minute walk (6MW) in persons with fibromyalgia (FM) and to determine an equation for predicting peak oxygen consumption (pVO2) from the distance covered in 6 minutes.

METHODS

Ninety-six women who met the American College of Rheumatology (ACR) criteria for FM were tested on the 6MW and the Fibromyalgia Impact Questionnaire (FIQ). A subset (n = 23) were tested on a separate day for pVO2 during a symptom-limited, incremental treadmill test. Twelve subjects repeated the 6MW five times over 10 days. Heart rate and rating of perceived exertion (RPE) were recorded for each walk. Intraclass correlations were used to determine the reliability of the 6MW. Validity was examined by correlating the 6MW with pVO2 and the FIQ. Body mass index (BMI) and 6MW were independent variables in a stepwise regression to predict pVO2.

RESULTS

A significant increase in distance occurred from Walk 1 to Walk 2 (p = 0.000) with the distance maintained on the remaining walks (p = 0.148) The correlations of the 6MW with the FIQ and pVO2 were -0.325 and 0.657, respectively. The regression equation to predict pVO2 from 6MW distance and BMI was: pVO2 (ml/kg/min) = 21.48 + (-0.4316 x BMI) + [0.0304 x distance(m)] (R = 0.76, R2 = 0.66).

CONCLUSION

When using the 6MW it is necessary to conduct a practice walk, with the second walk taken as the baseline measure. It was determined from the correlations that the 6MW cannot replace the FIQ as a measure of function. The 6MW may be used as an indicator of aerobic fitness, although obtaining VO2 by means of a graded exercise test is preferable.

Muscle oxygenation during incremental arm and leg exercise in men and women

The purpose of this study was to compare the rates of muscle deoxygenation in the exercising muscles during incremental arm cranking and leg cycling exercise in healthy men and women. Fifteen men and 10 women completed arm cranking and leg cycling tests to exhaustion in separate sessions in a counterbalanced order. Cardiorespiratory measurements were monitored using an automated metabolic cart interfaced with an electrocardiogram. Tissue absorbency was recorded continuously at 760 nm and 850 nm during incremental exercise and 6 min of recovery, with a near infrared spectrometer interfaced with a computer. Muscle oxygenation was calculated from the tissue absorbency measurements at 30%, 45%, 60%, 75% and 90% of peak oxygen uptake (VO2) during each exercise mode and is expressed as a percentage of the maximal range observed during exercise and recovery (%Mox). Exponential regression analysis indicated significant inverse relationships (P < 0.01) between %Mox and absolute VO2 during arm cranking and leg cycling in men (multiple R = -0.96 and -0.99, respectively) and women (R = -0.94 and -0.99, respectively). No significant interaction was observed for the %Mox between the two exercise modes and between the two genders. The rate of muscle deoxygenation per litre of VO2 was 31.1% and 26.4% during arm cranking and leg cycling, respectively, in men, and 26.3% and 37.4% respectively, in women. It was concluded that the rate of decline in %Mox for a given increase in VO2 between 30% and 90% of the peak VO2 was independent of exercise mode and gender.

Physiological and biomechanical responses during treadmill walking with graded loads

Eleven healthy men [mean (SD) for age, height, body mass and maximum oxygen consumption: 25.1 (3.0) years, 1.79 (0.06) m, 78.2 (10.5) kg and 56.9 (7.1) ml x kg(-1) x min(-1), respectively) completed two treadmill walking tests at their self-selected velocity while bilaterally carrying 15-kg and 20-kg loads (in a boxed container) for 4 min in front of the body. Each handle of the boxed container was fitted with a load cell so as to allow quantification of the load supported by each hand during load carriage. During the tests, oxygen uptake (VO2), heart rate (HR), and blood pressure (BP) were monitored using standardized procedures, and cardiac output (Qc) was measured using the carbon dioxide rebreathing method. Stroke volume (SV), arterio-venous oxygen difference (C(a-v)O2), rate pressure product (RPP) and total peripheral resistance (TPR) were calculated from the above measurements. The results showed that the two extremities sustained approximately 60% to 70% of the total load, with the balance being supported by the body. Significant increases (P < 0.05) in VO2, HR, Qc, and mean BP were observed during both of the load carriage walks compared to unloaded walking. However, SV, C(a-v)O2, RPP and TPR were unchanged (P > 0.05) during load carriage. Although VO2 was significantly higher during the 20-kg load carriage walk, no significant differences were observed between the two loads for any of the cardiovascular responses monitored. Contrary to our hypothesis, these results suggest that increasing the load from 15 kg to 20 kg during treadmill walking does not significantly increase the cardiovascular stress that occurs in healthy subjects.