Heart Rate Methods Can Be Valid for Estimating Intensity Spectrums of Oxygen Uptake in Field Exercise

PurposeQuantifying intensities of physical activities through measuring oxygen uptake (V̇O2) is of importance for understanding the relation between human movement, health and performance. This can in principle be estimated by the heart rate (HR) method, based on the linear relationship between HR and V̇O2 established in the laboratory. It needs, however, to be explored whether HR methods, based on HR-V̇O2 relationships determined in the laboratory, are valid for estimating spectrums of V̇O2 in field exercise. We hereby initiate such studies, and use cycle commuting as the form of exercise.MethodsTen male and ten female commuter cyclists underwent measurements of HR and V̇O2 while performing ergometer cycling in a laboratory and a normal cycle commute in the metropolitan area of Stockholm County, Sweden. Two models of individual HR-V̇O2 relationships were established in the laboratory through linear regression equations. Model 1 included three submaximal work rates, whereas model 2 also involved a maximal work rate. The HR-V̇O2 regression equations of the two models were then used to estimate V̇O2 at six positions of field HR: five means of quintiles and the mean of the whole commute. The estimations obtained were for both models compared with the measured V̇O2.ResultsThe measured quintile range during commuting cycling was about 45–80% of V̇O2max. Overall, there was a high resemblance between the estimated and measured V̇O2, without any significant absolute differences in either males or females (range of all differences: −0.03–0.20 L⋅min–1). Simultaneously, rather large individual differences were noted.ConclusionThe present HR methods are valid at group level for estimating V̇O2 of cycle commuting characterized by relatively wide spectrums of exercise intensities. To further the understanding of the external validity of the HR method, there is a need for studying other forms of field exercises.

Comparison of Physiological and Biomechanical Responses to Flat and Uphill Cross-Country Sit-Skiing in Able-Bodied Athletes

Purpose: To compare peak work rate (WRpeak) and associated physiological and biomechanical performance-determining variables between flat and uphill cross-country (XC) sit-skiing. Methods: Fifteen able-bodied male XC skiers completed 2 test sessions, each comprising four 4-minute submaximal stages, followed by an incremental test to exhaustion and a verification test in a sit-ski on a roller-ski treadmill. The test sessions were counterbalanced by the incline, being either 0.5% (FLAT) or 5% (UPHILL). The authors compared WRpeak and peak oxygen uptake, as well as physiological variables, rating of perceived exertion, gross efficiency, and cycle characteristics at identical submaximal work rate, between FLAT and UPHILL. Results: In UPHILL, WRpeak was 35% higher compared to FLAT (P < .001), despite no difference in peak oxygen uptake (P = .9). The higher WRpeak in UPHILL was achieved through more work per cycle, which was enabled by the twice as long poling time, compared to FLAT (P < .001). Submaximal gross efficiency was 0.5 to 2 percentage points lower in FLAT compared to UPHILL (P < .001), with an increasing difference as work rate increased (P < .001). Neither cycle rate nor work per cycle differed between inclines when compared at identical submaximal work rate (P > .16). Conclusions: The longer poling times utilized in uphill XC sit-skiing enable more work per cycle and better gross efficiency, thereby allowing skiers to achieve a higher WRpeak compared to flat XC sit-skiing. However, the similar values of peak oxygen uptake between inclines indicate that XC sit-skiers can tax their cardiorespiratory capacity similarly in both conditions.

28 Cardiorespiratory Regulation and Aerobic Fitness in Older People – A New Approach for Falls Interventions?

Introduction Guidelines for physical activity give recommendations for moderate to vigorous aerobic training 2-3 times per week. Aerobic exercise, like walking, shows mixed effects in regard to falls prevention. However, after high intensity exercise postural stability is decreased and better aerobic fitness might be relevant to minimize this fall risk in older individuals. So far, the association of aerobic fitness and falls has not been examined in older people. Feasible methodology is lacking. Aerobic fitness can be assessed measuring cardiorespiratory (heart rate [HR] and oxygen uptake [V’O2]) regulation in response to changing submaximal work rate (WR) intensities. For cycle ergometry (cycling) cardiorespiratory regulation correlated with aerobic fitness. Since treadmill walking (TMW) is closer to daily life activities, TMW is tested for feasibility in older people and compared to data during cycling. Methods 17 participants (65±6 years, 23.9±3.8 kg∙m-2) were tested for V’O2 and HR regulation during cycling (30W, 80W) and TMW (1.9 km·h-1, 5 km·h-1). Inclination during TMW was matched to WR during cycling. Additionally, WR was further increased until the first ventilatory threshold (VT1) was reached. Kinetics were assessed applying cross-correlation functions (CCF). Higher maxima in CCF (CCFmax () in a.u.) imply faster system responses. T-tests were applied to calculate differences between the exercise modes. Correlations were computed using Pearson tests. Results Significant differences for CCFmax (V’O2) were identified between cycling and TMW (0.51±0.10 vs. 0.45±0.08; p=0.032), but not for CCFmax (HR) (cycling: 0.62±0.13; TMW: 0.60±0.10; p=0.623). CCFmax (HR) during TMW correlated with V’O2 at VT1 during TMW (r=0.538, p=0.013). Discussion TMW is feasible to adequately determine cardiorespiratory regulation and correlated with aerobic fitness in older people and has a better applicability. Hence, cardiorespiratory regulation might be an important factor to assess in the context of falls.

The noninvasive simultaneous measurement of tissue oxygenation and microvascular hemodynamics during incremental handgrip exercise

Limb blood flow increases linearly with exercise intensity; however, invasive measurements of muscle microvascular blood flow during incremental exercise have demonstrated submaximal plateaus. We tested the hypotheses that 1) brachial artery blood flow (Q̇BA) would increase with increasing exercise intensity until task failure, 2) blood flow index of the flexor digitorum superficialis (BFIFDS) measured noninvasively via diffuse correlation spectroscopy would plateau at a submaximal work rate, and 3) muscle oxygenation characteristics (total-[heme], deoxy-[heme], and percentage saturation) measured noninvasively with near-infrared spectroscopy would demonstrate a plateau at a similar work rate as BFIFDS. Sixteen subjects (23.3 ± 3.9 yr, 170.8 ± 1.9 cm, 72.8 ± 3.4 kg) participated in this study. Peak power (Ppeak) was determined for each subject (1.8 ± 0.4 W) via an incremental handgrip exercise test. Q̇BA, BFIFDS, total-[heme], deoxy-[heme], and percentage saturation were measured during each stage of the exercise test. On a subsequent testing day, muscle activation measurements of the FDS (RMSFDS) were collected during each stage of an identical incremental handgrip exercise test via electromyography from a subset of subjects ( n = 7). Q̇BA increased with exercise intensity until the final work rate transition ( P < 0.05). No increases in BFIFDS or muscle oxygenation characteristics were observed at exercise intensities greater than 51.5 ± 22.9% of Ppeak. No submaximal plateau in RMSFDS was observed. Whereas muscle activation of the FDS increased until task failure, noninvasively measured indices of perfusive and diffusive muscle microvascular oxygen delivery demonstrated submaximal plateaus. NEW & NOTEWORTHY Invasive measurements of muscle microvascular blood flow during incremental exercise have demonstrated submaximal plateaus. We demonstrate that indices of perfusive and diffusive microvascular oxygen transport to skeletal muscle, measured completely noninvasively, plateau at submaximal work rates during incremental exercise, even though limb blood flow and muscle recruitment continued to increase.

Comparison of Cardio-respiratory Fitness and Anthropometric Characteristics between Teenage Swimmers and Non-swimmers

This study was conducted to compare cardio respiratory fitness indicators and anthropometric characteristics of national level teenage swimmers and a group of age and sex matched non-swimmers. 50 male and 54 female teenage swimmers who qualified for the School Nationals Meet were recruited to the study as well as similar numbers of age, sex and geographical area matched controls. VO2max was predicted from heart rate at a submaximal work load using a bicycle ergo meter (Monark Ergo medic 828E). Anthropometric measurements were obtained using standard equipment and procedures. Male swimmers had a significantly (p=0.0001) higher VO2max (mean 47.9 ± 7.6 ml/kg/min) compared to male controls (mean 31.7 ± 4.5 ml/kg/min) while female swimmers also had a significantly (p=0.0001) higher VO2max (mean 38.8 ± 5.8 ml/kg/min) than female controls (mean 27.7 ± 2.2 ml/kg/min). Male swimmers had a significantly higher shoulder (p=0.002) breadth (mean 34.5 ± 4.1 cm) than controls (mean 32.7 ± 3.1 cm). The hip circumference of male swimmers was also significantly greater (p=0.015) (mean 55.0 ± 4.4 cm) than controls (mean 56.4 ± 3.5 cm). Female swimmers also had significantly greater (p=0.001) shoulder breadth (mean 38.29 SD ± 2.7 cm) than controls (mean 35.9 ±1 .9). Hip circumference showed a reverse trend, controls had a significantly greater (p=0.01) hip circumference (mean 89.6 ± 3.8 cm) compared to female swimmers (mean 87.8 ± 1.9 cm). Therefore we conclude that there are significant differences in cardio-respiratory fitness and anthropometric parameters between teenage national level swimmers and non-swimmers in Sri Lanka.

Physiological and perceptual responses to incremental exercise testing in healthy men: effect of exercise test modality

In a randomized cross-over study of 15 healthy men aged 20–30 years, we compared physiological and perceptual responses during treadmill and cycle exercise test protocols matched for increments in work rate — the source of increased locomotor muscle metabolic and contractile demands. The rates of O2 consumption and CO2 production were higher at the peak of treadmill versus cycle testing (p ≤ 0.05). Nevertheless, work rate, minute ventilation, tidal volume (VT), breathing frequency (fR), inspiratory capacity (IC), inspiratory reserve volume (IRV), tidal esophageal (Pes,tidal) and transdiaphragmatic pressure swings (Pdi,tidal), peak expiratory gastric pressures (Pga,peak), the root mean square of the diaphragm electromyogram (EMGdi,rms) expressed as a percentage of maximum EMGdi,rms (EMGdi,rms%max), and dyspnea ratings were similar at the peak of treadmill versus cycle testing (p > 0.05). Ratings of leg discomfort were higher at the peak of cycle versus treadmill exercise (p ≤ 0.05), even though peak O2 consumption was lower during cycling. Oxygen consumption, CO2 production, minute ventilation, fR, Pes,tidal, Pdi,tidal and Pga,peak were higher (p ≤ 0.05), while VT, IC, IRV, EMGdi,rms%max, and ratings of dyspnea and leg discomfort were similar (p > 0.05) at all or most submaximal work rates during treadmill versus cycle exercise. Our findings highlight important differences (and similarities) in physiological and perceptual responses at maximal and submaximal work rates during incremental treadmill and cycle exercise testing protocols. The lack of effect of exercise test modality on peak work rate advocates for the use of this readily available parameter to optimize training intensity determination, regardless of exercise training mode.