Maximal lactate steady state,critical power and EMG during cycling

We hypothesised that: (1) the maximal lactate steady state (MLSS), critical power (CP) and electromyographic fatigue threshold (EMG_FT) occur at the same power output in cycling exercise, and (2) exercise above the power output at MLSS (P-MLSS) results in continued increases in oxygen uptake (V˙O₂), blood lactate concentration ([La]) and integrated electromyogram (iEMG) with time. Eight healthy subjects [mean (SD) age 25 (3) years, body mass 72.1 (8.2) kg] performed a series of laboratory tests for the determination of MLSS, CP and EMG_FT. The CP was determined from four exhaustive trials of between 2 and 15 min duration. The MLSS was determined as the highest power output at which the increase in blood [La] was less than 1.0 mM across the last 20 min of a series of 30-min trials. The EMG_FT was determined from four trials of 2 min duration at different power outputs. The surface electromyogram was recorded continuously from the vastus lateralis muscle. The CP was significantly higher than the P-MLSS [242 (25) vs. 222 (23) W; P<0.05], although the two variables were strongly correlated (r=0.95; P<0.01). The EMG_FT could not be determined in 50% of the subjects. Blood [La], V˙O₂ and minute ventilation all increased significantly with time for exercise at power outputs above the P-MLSS. In conclusion, the P-MLSS, and not the CP, represents the upper limit of the heavy exercise domain in cycling. During exercise above the P-MLSS, there is no association between changes in iEMG and increases in V˙O₂ and blood [La] with time. Electronic Publication     

Effect of prior heavy arm and leg exercise on V˙O<Subscript>2</Subscript> kinetics during heavy leg exercise

The aim of the present study was to examine the effect of prior exercise at a remote site on the V˙O₂ kinetics during subsequent heavy cycle exercise using a model that allowed us to discriminate between the V˙O₂ fast and slow component responses. Ten male subjects completed a constant-load exercise of 6 min cycling at 90% of the V˙O₂peak in three conditions: without prior exercise (LE-C), after heavy cycling exercise (6 min at 90% of the V˙O₂peak) (LE-L) and after heavy arm-cranking exercise (6 min at 90% of the arm V˙O₂peak) (LE-A). Subjects performed four repetitions of each exercise protocol, separated by at least 1 day. V˙O₂ was measured on a breath-by-breath basis and V˙O₂ kinetics were determined with a biexponential model. There were no significant differences in the V˙O₂ fast component parameters between LE-C, LE-L and LE-A. However, the V˙O₂ slow component amplitude was significantly reduced in LE-L and LE-A compared to LE–C, but the reduction was less pronounced in LE-A [the value of the V˙O₂ slow exponential term at the end of exercise, A ₂′, was 657 (SD 200) ml^.min^–1 in LE-C versus 384 (SD 136) ml^.min^–1 in LE-L and 551 (SD 169) ml^.min^–1 in LE-A; P<0.05]. The results of this study demonstrate that prior heavy arm exercise alters V˙O₂ kinetics during cycling exercise by reducing the V˙O₂slow component amplitude, though this reduction is smaller than the reduction observed following prior heavy leg exercise. These data indicate that the primary factor causing changes in the V˙O₂ kinetics is probably located in the involved muscle. Electronic Publication     

Perceived exertion related to heart rate and blood lactate during arm and leg exercise

Summary To compare some psychophysiological responses to arm exercise with those to leg exercise, an experiment was carried out on electronically braked bicycle ergometers, one being adapted for arm exercise. Eight healthy males took part in the experiment with stepwise increases in exercise intensity every 4 min: 40—70—100—150—200 W in cycling and 20—35—50—70—100 W in arm cranking. Towards the end of each 4 min period, ratings of perceived exertion were obtained on the RPE scale and on a new category ratio (CR) scale: heart rate (HR) and blood lactate accumulation (BL) were also measured. The responses obtained were about twice as high or more for arm cranking than for cycling. The biggest difference was found for BL and the smallest for HR and RPE. The incremental functions were similar in both activities, with approximately linear increases in HR and RPE and positively accelerating functions for CR (exponents about 1.9) and BL (exponents 2.5 and 3.3 respectively). When perceived exertion (according to the CR scale) was set as the dependent variable and a simple combination of HR and BL was used as the independent variable, a linear relationship was obtained for both kinds of exercise, as has previously been found in cycling, running, and walking. The results thus give support for the following generalization: For exercise of a steady state type with increasing loads the incremental curve for perceived exertion can be predicted from a simple combination of HR and BL. This study was supported by a research grant from The Bank of Sweden Tercentenary Foundation No. 85/291     

Oxygen uptake kinetics during high-intensity arm and leg exercise

The purpose of the present study was to examine the oxygen uptake kinetics during heavy arm exercise using appropriate modelling techniques, and to compare the responses to those observed during heavy leg exercise at the same relative intensity. We hypothesised that any differences in the response might be related to differences in muscle fibre composition that are known to exist between the upper and lower body musculature. To test this, ten subjects completed several bouts of constant-load cycling and arm cranking exercise at 90% of the mode specific V(O(2)) peak. There was no difference in plasma [lactate] at the end of arm and leg exercise. The time constant of the fast component response was significantly longer in arm exercise compared to leg exercise (mean+/-S.D., 48+/-12 vs. 21+/-5 sec; P < 0.01), while the fast component gain was significantly greater in arm exercise (12.1+/-1.0 vs. 9.2+/-0.5 ml min(-1) W(-1); P < 0.01). The V(O(2)) slow component emerged later in arm exercise (126+/-27 vs. 95+/-20 sec; P < 0.01) and, in relative terms, increased more per unit time (5.5 vs. 4.4% min(-1); P < 0.01). These differences between arm crank and leg cycle exercise are consistent with a greater and/or earlier recruitment of type II muscle fibres during arm crank exercise.     

Voluntary changes in leg cadence modulate arm cadence during simultaneous arm and leg cycling

Although there is some evidence showing that neural coupling plays an important role in regulating coordination between the upper and lower limbs during walking, it is unclear how tightly the upper and lower limbs are linked during rhythmic movements in humans. The present study was conducted to investigate how coupling of both limbs is coordinated during independent rhythmic movement of the upper and lower limbs. Ten subjects performed simultaneous arm and leg cycling (AL cycling) at their preferred cadences without feedback for 10 s, and then were asked to voluntarily change the cadence (increase, decrease, or stop) of arm or leg cycling. Leg cycling cadence was not affected by voluntary changes in arm cadence. By contrast, arm cycling cadence was significantly altered when leg cycling cadence was changed. These results suggest the existence of a predominant lumbocervical influence of leg cycling on arm cycling during AL cycling.     

Effects of prior heavy exercise,prior sprint exercise and passive warming on oxygen uptake kinetics during heavy exercise in humans

Prior heavy exercise (above the lactate threshold, Th_la) increases the amplitude of the primary oxygen uptake (VO₂) response and reduces the amplitude of the VO₂ slow component during subsequent heavy exercise. The purpose of this study was to determine whether these effects required the prior performance of an identical bout of heavy exercise, or if prior short-duration sprint exercise could cause similar effects. A secondary purpose of this study was to determine the effect of elevating muscle temperature (through passive warming) on VO₂ kinetics during heavy exercise. Nine male subjects performed a 6-min bout of heavy exercise on a cycle ergometer 6 min after: (1) an identical bout of heavy exercise; (2) a 30-s bout of maximal sprint cycling; (3) a 40-min period of leg warming in a hot water bath at 42°C. Prior sprint exercise elevated blood [lactate] prior to the onset of heavy exercise (by ≅5.6 mM) with only a minor increase in muscle temperature (of ≅0.7°C). In contrast, prior warming had no effect on baseline blood lactate concentration, but elevated muscle temperature by ≅2.6°C. Both prior heavy exercise and prior sprint exercise significantly increased the absolute primary VO₂ amplitude (by ≅230 ml·min^–1 and 260 ml·min^–1, respectively) and reduced the amplitude of the VO₂ slow component (by ≅280 ml·min^–1 and 200 ml·min^–1, respectively) during heavy exercise, whereas prior warming had no significant effect on the VO₂ response. We conclude that the VO₂ response to heavy exercise can be markedly altered by both sustained heavy-intensity submaximal exercise and by short-duration sprint exercise that induces a residual acidosis. In contrast, passive warming elevated muscle temperature but had no effect on the VO₂ response. Electronic Publication     

Metabolic responses to light arm and leg exercise when sitting

Summary Seven male subjects performed progressive exercises with a light work load on an upper limb or bicycle ergometer in the sitting position. At any comparable work load above zero, arm exercise induced higher oxygen uptake, ventilation, heart rate, oxygen pulse, respiratory rate and tidal volume than leg exercise. At similar levels of above 0.45 1 · min^–1, heart rate and ventilation were higher during arm exercise. A close linear relationship between carbon dioxide output and oxygen uptake was observed during both arm and leg exercises, the slope for arm work being steeper. The ventilatory equivalent for gradually decreased during both types of exercise. The ventilatory equivalent for remained constant (arm) while it rose (leg) to a peak at 9.8 W and then gradually decreased. Ventilation in relation to tidal volume had a linear relationship with leg exercise, but became curvilinear with arm exercise after tidal volume exceeded 1100ml. The observed differences in response between arm and leg exercises at a given work load appear to be influenced by differences in sympathetic outflow due to the greater level of static contraction of the relatively small muscle groups required by arm exercise.     

Oxygen uptake kinetics during severe intensity running and cycling

The purpose of this study was to investigate the effect of exercise mode on the characteristics of the oxygen uptake ( V̇O₂) response to exercise within the severe intensity domain. Twelve participants each performed a treadmill running test and a cycle ergometer test to fatigue at intensities selected to elicit a mode-specific V̇O₂max and to cause fatigue in ~5 min. The tests were at 234 (30) m·min⁻¹ and 251 (59) W, and times to fatigue were 297 (15) s and 298 (14) s, respectively. The overall rapidity of the V̇O₂response was influenced by exercise mode [ V̇O₂max was achieved after 115 (20) s in running versus 207 (36) s in cycling; p<0.01]. V̇O₂ responses were fit to a three-phase exponential model. The time constant of the primary phase was faster in treadmill tests than in cycle ergometer tests [14 (6) s versus 25 (4) s; p<0.01], and the amplitude of the primary phase was greater in running than in cycling when it was expressed in absolute terms [2327 (393) ml·min⁻¹ versus 2036 (301) ml·min⁻¹; p=0.02] but not when it was expressed as a percentage of the total increase in V̇O₂ [86 (6)% versus 82 (6)%; p=0.09]. When quantified as the difference between the end-exercise V̇O₂ and the V̇O₂ at 2 min, the amplitude of the slow component was ~40% smaller in running [177 (92) ml·min⁻¹ versus 299 (153) ml min⁻¹; p=0.03]. It is concluded that exercise modality affects the characteristics of the V̇O₂ response at equivalent intensities in the severe domain.     

A comparison of two time-domain analysis procedures in the determination of .VO(2) kinetics by pseudorandom binary sequence exercise testing

The purpose of this study was to apply and compare two time-domain analysis procedures in the determination of oxygen uptake (V˙O₂) kinetics in response to a pseudorandom binary sequence (PRBS) exercise test. PRBS exercise tests have typically been analysed in the frequency domain. However, the complex interpretation of frequency responses may have limited the application of this procedure in both sporting and clinical contexts, where a single time measurement would facilitate subject comparison. The relative potential of both a mean response time (MRT) and a peak cross-correlation time (PCCT) was investigated. This study was divided into two parts: a test-retest reliability study (part A), in which 10 healthy male subjects completed two identical PRBS exercise tests, and a comparison of the V˙O₂ kinetics of 12 elite endurance runners (ER) and 12 elite sprinters (SR; part B). In part A, 95% limits of agreement were calculated for comparison between MRT and PCCT. The results of part A showed no significant difference between test and retest as assessed by MRT [mean (SD) 42.2 (4.2) s and 43.8 (6.9) s] or by PCCT [21.8 (3.7) s and 22.7 (4.5) s]. Measurement error (%) was lower for MRT in comparison with PCCT (16% and 25%, respectively). In part B of the study, the V˙O₂ kinetics of ER were significantly faster than those of SR, as assessed by MRT [33.4 (3.4) s and 39.9 (7.1) s, respectively; P<0.01] and PCCT [20.9 (3.8) s and 24.8 (4.5) s; P<0.05]. It is possible that either analysis procedure could provide a single test measurement of V˙O₂ kinetics; however, the greater reliability of the MRT data suggests that this method has more potential for development in the assessment of V˙O₂ kinetics by PRBS exercise testing. Electronic Publication     

The effect of prolonged submaximal exercise on gas exchange kinetics and ventilation during heavy exercise in humans

This study compared ventilation, gas exchange (oxygen uptake, V̇O₂) and the surface electromyogram (EMG) activity of four major lower limb muscles during heavy exercise before (Pre-Ex) and after (Post-Ex) a sustained 90-min cycling exercise at 60% V̇O_2peak. The 90-min exercise was incorporated under the hypothesis that sustained exercise would alter substrate availability in the second exercise bout causing differences in fibre recruitment patterns, gas exchange and ventilation. Nine trained male subjects [V̇O_2peak=60.2 (1.7) ml·kg⁻¹·min⁻¹] completed two identical 6-min bouts of cycling performed at high intensity [~90% V̇O_2peak; 307 (6) W, mean (SE)]. Ventilation and gas exchange were measured breath-by-breath and the EMG was recorded during the last 12 s of each minute of the two 6-min bouts. EMG signals were analysed to determine integrated EMG (iEMG) and mean power frequency (MPF). V̇O₂ at min 3 and min 6 in Post-Ex were significantly higher (i.e., +201 and 141 ml·min⁻¹, respectively, P<0.05) than in Pre-Ex but there was a ~25% decrease of the slow component, taken as the difference between min 6 and min 3 [187 (27) vs 249 (35) ml·min⁻¹, respectively, P<0.05]. The greater whole-body V̇O₂ after 3 min of exercise in Post-Ex was not accompanied by clear alterations in the iEMG and MPF of the examined leg muscles. Ventilation and heart rate were elevated (~12–16 l·min⁻¹ and ~10 beats·min⁻¹, respectively, P<0.05) as were the ratios V̇ _E/O₂ and V̇ _E/V̇CO₂ in the Post-Ex tests. It was concluded that the V̇O₂ and ventilation responses to high-intensity exercise can be altered following prolonged moderate intensity exercise in terms of increased amplitude without associated major changes in either iEMG or MPF values among conditions.     

Oxygen uptake kinetics during severe exercise: a comparison between young and older men

This study examined the relationship between the slow component of oxygen uptake (VO2) kinetics and muscle electromyography (EMG) during severe exercise in nine young (21.7+/-0.9 yr) and nine older (71.6+/-0.8 yr) men. Oxygen uptake (VO2) and surface EMG activity of the left vastus lateralis muscle were measured during a 7-min square-wave bout of severe exercise on a cycle ergometer. The absolute amplitude of the VO2 slow component was greater and occurred approximately 60 s earlier in the young compared to older subjects. However, the rate of increase in the slow component, expressed as a percentage of the total VO2 response per unit time, was not different between young and older subjects (young: 4.8+/-0.5%.min(-1); older: 4.9+/-0.6%.min(-1)). The mean power frequency (MPF) of the EMG increased significantly during the slow component phase of exercise by 6.4+/-1.0% in the young and by 5.4+/-0.7% in the older group and this rise was not significantly different between the two groups. These results indicate that normal ageing may not alter the VO2 slow component (measured as the rate of increase in VO2) and that this finding may be related to similar muscle fibre recruitment patterns in the two groups during severe-intensity exercise.     

One-legged endurance training: leg blood flow and oxygen extraction during cycling exercise

Aim: As a consequence of enhanced local vascular conductance, perfusion of muscles increases with exercise intensity to suffice the oxygen demand. However, when maximal oxygen uptake (VO₂max) and cardiac output are approached, the increase in conductance is blunted. Endurance training increases muscle metabolic capacity, but to what extent that affects the regulation of muscle vascular conductance during exercise is unknown. Methods: Seven weeks of one‐legged endurance training was carried out by twelve subjects. Pulmonary VO₂ during cycling and one‐legged cycling was tested before and after training, while VO₂ of the trained leg (TL) and control leg (CL) during cycling was determined after training. Results: VO₂max for cycling was unaffected by training, although one‐legged VO₂max became 6.7 (2.3)% (mean ± SE) larger with TL than with CL. Also TL citrate synthase activity was higher [30 (12)%; P < 0.05]. With the two legs working at precisely the same power during cycling at high intensity (n = 8), leg oxygen uptake was 21 (8)% larger for TL than for CL (P < 0.05) with oxygen extraction being 3.5 (1.1)% higher (P < 0.05) and leg blood flow tended to be higher by 16.0 (7.0)% (P = 0.06). Conclusion: That enhanced VO₂max for the trained leg had no implication for cycling VO₂max supports that there is a central limitation to VO₂max during whole‐body exercise. However, the metabolic balance between the legs was changed during high‐intensity exercise as oxygen delivery and oxygen extraction were higher in the trained leg, suggesting that endurance training ameliorates blunting of leg blood flow and oxygen uptake during whole‐body exercise.     

Oxygen uptake kinetics during moderate,heavy and severe intensity "submaximal" exercise in humans: the influence of muscle fibre type and capillarisation

The purpose of the present study was to test the hypothesis that muscle fibre type influences the oxygen uptake (V˙O₂) on-kinetic response (primary time constant; primary and slow component amplitudes) during moderate, heavy and severe intensity sub-maximal cycle exercise. Fourteen subjects [10 males, mean (SD) age 25 (4) years; mass 72.6 (3.9) kg; V˙O_2peak 47.9 (2.3) ml kg⁻¹ min⁻¹] volunteered to participate in this study. The subjects underwent a muscle biopsy of the vastus lateralis for histochemical determination of muscle fibre type, and completed repeat 'square-wave' transitions from unloaded cycling to power outputs corresponding to 80% of the ventilatory threshold (VT; moderate exercise), 50% (heavy exercise) and 70% (severe exercise) of the difference between the VT and V˙O_2peak. Pulmonary V˙O₂ was measured breath-by-breath. The percentage of type I fibres was significantly correlated with the time constant of the primary V˙O₂ response for heavy exercise (r=−0.68). Furthermore, the percentage of type I muscle fibres was significantly correlated with the gain of the V˙O₂ primary component for moderate (r=0.65), heavy (r=0.57) and severe (r=0.57) exercise, and with the relative amplitude of the V˙O₂ slow component for heavy (r=−0.74) and severe (r=−0.64) exercise. The influence of muscle fibre type on the V˙O₂ on-kinetic response persisted when differences in aerobic fitness and muscle capillarity were accounted for. This study demonstrates that muscle fibre type is significantly related to both the speed and the amplitudes of the V˙O₂ response at the onset of constant-load sub-maximal exercise. Differences in contraction efficiency and oxidative enzyme activity between type I and type II muscle fibres may be responsible for the differences observed. Electronic Publication     

A comparison of the relation between oxygen uptake and heart rate during different styles of aerobic dance and a traditional step test in women

The oxygen uptake and heart rate in various styles of dance and in a graded step test have been compared in ten healthy women aged [mean (SD)] 34 (5) years. Dance was choreographed into progressively more energetic sequences typical of community classes, and videotaped. Oxygen uptake was assessed using a respirometer carried in a back-pack. Each of the two tests (dance and step) took 15–20 min and measurements were made in randomised balanced order on the same day. The mean oxygen costs of dance ranged from 1.29 l · min^–1 for low impact style to 1.83 1 · min^–1 for high impact style with arm work; mean heart rates were 135 and 174 beats · min^–1 respectively. Low impact dance raised heart rates above 60% of predicted maximum and so would provide training; during high impact dance recorded heart rates sometimes exceeded recommended safe limits. The addition of arm work significantly increased heart rates in both high and low impact dance but when oxygen pulses for each style of dance were compared no significant differences attributable to arm work were found. Moreover calculated differences between oxygen uptakes in stepping and dance at the same heart rates (those recorded during dance) were not significant for any of the four styles. Analysis of variance confirmed that neither arm work nor impact contributed significantly to the differences, so there was no evidence that these forms of dance change the normal relation between heart rate and oxygen uptake found in dynamic activities with large muscle groups such as stepping.     

Prediction of maximal oxygen uptake from the ratings of perceived exertion and heart rate during a perceptually-regulated sub-maximal exercise test in active and sedentary participants

This study assessed whether the accuracy of predicting maximal oxygen uptake (VO2max) from sub-maximal heart rate (HR) and ratings of perceived exertion (RPE) values was moderated by gender and habitual activity. In total, 27 men and 18 women completed two GXTs to determine VO2max and three perceptually-regulated GXTs, incremented by RPE 9, 11, 13, 15 and 17. The RPE and HR were individually regressed against VO2max (approximately 0.96) to enable predictions of VO2max. The VO2max was predicted from three RPE ranges (9-17, 9-15, 9-13). The RPE ranges were extrapolated to RPE(19), RPE(20) and age-predicted maximal HR (HRmax(pred)). ANOVA revealed no differences between measured and predicted VO2max (P > 0.05) when the RPE range 9-17 was extrapolated to RPE(19) and HRmax(pred). Extrapolation of RPE 9-17 to RPE(20) overestimated VO2max (P < 0.05), but no differences were observed when predicted from the RPE ranges 9-15 and 9-13. The prediction of VO2max was not moderated by gender or activity status. Hierarchical regression analysis revealed that HR explained additional variance in VO2max when added to the RPE (2%). Hierarchical multiple regression analysis also indicated that VO2max was significantly correlated with power output at sub-maximal RPE values of 13 and 15 (P < 0.01) in men and women. The addition of HRmax(pred) improved the accuracy of the prediction equation for men (P = 0.05) but not for women. The study confirmed the validity of estimating VO2max from perceptually-regulated, sub-maximal GXT and indicated the potential utility of regression analysis to gauge appropriate sub-maximal exercise intensities.     

Short- and long-term effects of a single bout of exercise on heart rate variability: comparison between constant and interval training exercises

Heart rate variability (HRV) was assessed during the short- (within 1 h) and long- (within 48 h) term recovery following a single bout of either constant (CST) or interval training (SWEET) exercise performed at the same total physical work [9.4 (0.3) kJ kg^–1]. R-R intervals, systolic (SAP) and diastolic (DAP) arterial pressures were recorded in supine and upright positions before and 1, 24 and 48 h after the termination of the exercises in ten male subjects [mean (SEM), age 24.6 (0.6) years, height 177.2 (1.1) cm and body mass 68.5 (0.9) kg]. The parameters were also recorded in the supine position during the first 20 min following the end of the exercise. Spectral analysis parameters of HRV [total (TP), low- (LF), and high- (HF) frequency power, and LF/TP, HF/TP and LF/HF ratios] were determined over 5 min during each phase. Except for higher HF values in both supine and upright positions during the first hour following CST compared with SWEET, cardiovascular and HRV analysis responses were of the same magnitude after their termination. R-R intervals, TP, and HF/TP were significantly decreased while LF/TP and LF/HF were significantly increased during the early recovery, when compared with control values. This could be a response to the significant decrease in SAP and DAP at this time. Twenty-four and 48 h after the end of the exercise, HRV parameters were at the same levels as before exercises in the supine posture, but a persistent tachycardia continued to be observed in the upright posture, together with reduced TP values, showing that cardiovascular functions were still disturbed. The short-term HRV recovery seemed dependent on the type of exercise, contrary to the long-term recovery.