Relationships between oxygen consumption and heart rate in transitory and steady states of exercise and during recovery: influence of type of exercise

Relationships between percentage of maximal oxygen consumption ( ) and percentage of maximal heart rate reserve ( ) were compared during steady states of exercise (S), transitory states of exercise (T) and a 5-min recovery period (R). Male adults [mean age 27 (SD 10) years] were studied exercising on a treadmill (TR, ), cycle ergometer (CE, ) and arm traction bench (ATB, ). The exercise intensity was adjusted according to the subjects in order to reach exhaustion in 4–5 steps of 2 min (ATB) or 3 min (TR, CE). The 1st min of each stage was considered as T and the last minute of each stage as S. The oxygen consumption ( ) and heart rate ( ) were recorded simultaneously. Significant correlations were observed for each type of exercise and for each state between and ( range 0.87–1.00). During T and R, the versus relationships were laterally shifted, suggesting a resetting of control mechanisms. In S, the intercept was greater than in T and R; in T, the slope was greater than in S and R. The could be predicted from individual versus relationships during T and R as is usually done in S using specific equations. Taking into consideration the average relationships established on the three ergometers, the standard error of the predicted during S and T reached 10%–20% and 22%–38% in R. During exercise, the higher the intensity the better was the prediction of from ( range 0.46–0.60, ). Therefore except at high exercise intensities, it was found that individual relationships had to be used to obtain an accurate estimation of .     

The relationship between preferred and optimal positioning during submaximal cycle ergometry

This study was designed to determine how changes in oxygen uptake ( O₂) and heart rate (HR) during submaximal cycle ergometry were determined by changes in cycle geometry and/or lower-limb kinematics. Fourteen trained cyclists [Mean (SD): age, 25.5 (6.4) years; body mass 74.4 (8.8) kg; peak O₂, 4.76 (0.79) l. min^?1 peak] were tested at three seat-tube angles (70°, 80°, 90°) at each of three trunk angles (10°, 20°, 30°) using a modified Monark cycle ergometer. All conditions were tested at a power output corresponding to 95% of the O₂ at each subject's ventilatory threshold while pedalling at 90 rpm and using aerodynamic handlebars. Sagittal-view kinematics for the hip, knee, and ankle joints were also recorded for all conditions and for the subjects' preferred positioning on their own bicycles. No combination of seat-tube and trunk angle could be considered optimal since many of the nine conditions elicited statistically similar mean O₂ and HR values. Mean hip angle (HA) was the only kinematic variable that changed consistently across conditions. A regression relationship was not observed between mean O₂ or HR and mean hip angle values (P?>?0.45). Significant curvilinear relationships were observed, however, between Δ O₂ ( O₂???minimum O₂) and ΔHA (mean HA???preferred HA) using the data from all subjects (R?=?0.45, SEE?=?0.13 l?.?min^?1) and using group mean values (R?=?0.93, SEE?=?0.03 l?.?min^?1). In both cases Δ O₂ minimized at ΔHA?=?0, which corresponded to the subjects' preferred HA from their own bicycles. Thus, subjects optimized their O₂ cost at cycle geometries that elicited similar lower-limb kinematics as the preferred geometries from their own bicycles.     

Exercise-induced oxyhemoglobin desaturation and pulmonary diffusing capacity during high-intensity exercise

The purpose of this investigation was to examine if exercise-induced arterial oxyhemoglobin desaturation selectively observed in highly trained endurance athletes could be related to differences in the pulmonary diffusing capacity (D _L) measured during exercise. The D _L of 24 male endurance athletes was measured using a 3-s breath-hold carbon monoxide procedure (to give D _LCO) at rest as well as during cycling at 60% and 90% of these previously determined ${\dot V}$ O_2max. Oxyhemoglobin saturation (S _aO₂%) was monitored throughout both exercise protocols using an Ohmeda Biox II oximeter. Exercise-induced oxyhemoglobin desaturation (DS) (S _aO₂%? ${\dot V}$ O_2max) was observed in 13 subjects [88.2 (0.6)%] but not in the other 11 nondesaturation subjects [NDS: 92.9 (0.4)%] (P?≤?0.05), although ${\dot V}$ O_2max was not significantly different between the groups [DS: 4.34 (0.65) l?/?min vs NDS: 4.1 (0.49) l?/?min]. At rest, no differences in either D _LCO [m1 CO?·?mmHg^?1?·?min^?1: 41.7 (1.7) (DS) vs 41.1 (1.8) (NDS)], D _LCO?/ ${\dot V}$ _A [8.2 (0.4) (DS) vs 7.3 (0.9) (NDS)], MVV [l?/?min: 196.0 (10.4) (DS) vs 182.0 (9.9) (NDS)] or FEV₁/FVC [86.3 (2.2) (DS) vs 82.9 (4.7) (NDS)] were found between groups (P?≥?0.05). However, ${\dot V}$ _E?/ ${\dot V}$ O₂ at ${\dot V}$ O_2max was lower in the DS group [33.0 (1.1)] compared to the NDS group [36.8 (1.5)] (P?≤?0.05). Exercise D _LCO (m1 CO?·?mmHg^?1?·?min^?1?) was not different between groups at either 60% ${\dot V}$ O_2max [DS: 55.1 (1.4) vs NDS: 57.2 (2.1)] or at 90% ${\dot V}$ O_2max [DS: 61.0 (1.8) vs NDS: 61.4 (2.9)]. A significant relationship (r?=?0.698) was calculated to occur between S _aO₂% and ${\dot V}$ _E?/ ${\dot V}$ O₂ during maximal exercise. The present findings indicate that the exercise-induced oxyhemoglobin desaturation seen during submaximal and near-maximal exercise is not related to differences in D _L, although during maximal exercise S _aO₂ may be limited by a relatively lower exercise ventilation.     

Determinants of maximal instantaneous muscle power in women aged 50–75 years

The present study aimed at analysing the age-related decline in maximal muscle power (W˙) in 52 sedentary healthy women aged between 50 and 75 years to determine whether force or velocity is the major determinant. Maximal muscle power was estimated from two types of vertical jumps, squatting (SJ) and counter‐movement (CmJ), performed on a force platform. It was obtained by measuring the vertical force (F _opt) applied to the body centre of gravity and calculating the corresponding vertical velocity ( _opt). An age-related decline in absolute W˙ was statistically significant in all the conditions examined and in both peak W˙ and average power ( ) values. The decrease in _opt was also statistically significant. Also F_opt declined but this reduction was not statistically significant with the exception of the average value in CmJ. Not surprisingly the highest W˙ were obtained in CmJ, and the difference in power production between the two types of jump showed an age-related decrement only in . The main finding of the study was the demonstration that _opt was the critical determinant of the age-related decline in W˙ in healthy elderly women.     

A 5-min running field test as a measurement of maximal aerobic velocity

Based on a theoretical approach from world record running data, we have previously calculated that the most suitable duration for measuring maximal aero-bic velocity (v _amax) by a field test was 5 min (v _amax(5)). The aim of this study was, therefore, to check this hypothesis on 48 men of various levels of physical fitness by comparing (v _max(5)) with (v _amax) determined at the last step of a progressive treadmill exercise test when the subject felt exhausted (v _amax(t)) and during a test on a running track, behind a cyclist (following an established protocol) (v _amax(c)). For each test, ( O_2max) was also measured by a direct method on a treadmill ( O_2max(t)) and calculated by an equation for field tests ( O_2max(5) and O_2max(c)). The V _amax(5) [17.1 (SD 2.2) km?·?h^?1] and (v _amax(c)) [(18.2 (SD 2.4) km?·?h^?1] were significantly higher than (v _amx(t)) [16.9 (SD 2.6) km?·?h^?1; P?v _amax(t))?was strongly correlated with (v _amax(5)) (r?=?0.94) and (v _amax(c)) (r?=?0.95) (P?v _amax(5)) and track performances were found in the runners (n?=?9) with experience over a distance of 3,000 m. The O_2max(5) and ( O_2max(c)) were higher than O_2max(t) (+?5.0% and?+?13.7%, respectively; P? O_2max(t) was highly correlated with v _amax(5) (r?=?0.90; P?v _amax and to a lesser degree on O_2max.     

Relationship of pulmonary diffusing capacity (D L ) and cardiac output (\dot Q_c ) in exercise

The present study was designed to investigate the interrelationships of pulmonary diffusing capacity for CO ( \(D_{L_{{\text{CO}}} } \) ), pulmonary capillary blood flow ( \(\dot Q_c \) ), oxygen uptake ( \(\dot V_{{\text{O}}_{\text{2}} } \) ), and related functions in exercise. Six young adult men were tested on a bicycle ergometer on 9–20 occasions at various intensities of exercise up to the maximal level that could be sustained for 5 min. Measurements at each exercise level included work load (kgm/min), heart rate (HR), minute ventilation (V _I ), \(\dot Q_c \) , \(D_{L_{{\text{CO}}} } \) , and \(\dot V_{{\text{O}}_{\text{2}} } \) . Using regression analysis, it was established that \(\dot Q_c \) and D _{L CO} increased linearly with \(\dot V_{{\text{O}}_{\text{2}} } \) throughout the work range in each subject and no tendency toward a plateau was observed. While the maximal value varied from subject to subject, there was no difference between individuals in the coefffcient describing the relationship of D _L and \(\dot Q_c \) to \(\dot V_{{\text{O}}_{\text{2}} } \) . Combining all subjects, D _L was found to increase linearly with \(\dot Q_c \) the regression equation being: $$D_L = 26.4 + 1.03{\text{ }}\dot Q_c ,{\text{ }}r = .79$$ These results suggest that high-intensity short-duration exercise (5 min) is probably not limited by either of these functions in normals.     

Thermoregulatory responses of prepubertal boys and young men during moderate exercise

Seven prepubertal boys (aged 10–11 years)?and eleven young men (aged 21–25 years), matched for skinfold thickness and maximal oxygen uptake ( O_2max) per unit of mass, cycled at an intensity of approximately 40% O_2max for 45 min in a warm condition (30?°C, 45% relative humidity). During exercise no age-related differences were observed for the increases in rectal temperature (T _re) and heart rate (HR), although the absolute T _re and HR were significantly greater for the boys because of a higher initial baseline (P??2?·?45 min^?1; P? _sw) on chest, back, and forearm were significantly lower for the boys (P??2; P? _sw in the boys was due to a lower output per activated sweat gland, even though they had a higher activated sweat gland density regardless of site. In contrast, cutaneous blood flow by laser Doppler flowmetry (LDF) in the boys was significantly greater on the chest and back, compared to the men (P?P?P? _sw, compared to the young men. It was concluded that during moderate exercise in an air temperature at 30?°C, prepubertal boys could thermoregulate as efficiently as young men by greater vasodilatation on their trunk despite lower _sw. Furthermore regional differences may exist in the maturation-related modification of vasodilatation.     

Relationship of critical velocity to marathon running performance

The purpose of this investigation was to evaluate the critical velocity (CV) test for prediction of marathon running performance. Twelve subjects [mean age (SD) = 29 (4) years; mean body mass = 63 (13) kg] were tested for CV and completed the 1994 New York City Marathon. The CV (m?·?s^?1) was determined from times to exhaustion at four treadmill running velocities. In addition, peak oxygen consumption ( O _{2 peak}; ml?·?kg^?1?·?min^?1) and ventilatory threshold (Th_vent) were determined from an incremental treadmill test. The Th_vent was calculated using bi-segmental linear regression and was expressed as the velocity (m?·?s^?1) at Th_vent. Separate simple linear regression analyses showed that marathon time [MT; mean (SD) = 231.9 (27.4) min] correlated more highly with CV [MT = 445.3 – 50.3 (CV); r ² = 0.76, SEE = 14.1 min] than either O_2peak [MT = 390.7 – 2.7 ( O_2peak); r ² = 0.51, SEE = 20.1 min] or Th_vent [MT = 353.5 – 30.1 (Th_vent) r ² = 0.28, SEE = 27.4 min]. A stepwise regression analysis resulted in CV (entered first) and Th_vent being included in the prediction equation [MT = 443.5 – 78.9 (CV) + 34.3 (Th_vent), R ² = 0.88, SEE = 10.7 min], while O_2peak was not included. These preliminary data indicate that the CV test may be an attractive field test for assessing marathon performance capabilities.     

Metabolic and performance adaptations to interval training in endurance-trained cyclists

This study examined the effects of sustained high-intensity interval training (HIT) on the athletic performances and fuel utilisation of eight male endurance-trained cyclists. Before HIT, each subject undertook three baseline peak power output ${\dot W}_{\rm peak}$ tests and two simulated 40-km time-trial cycling performance (TT₄₀) tests, of which the variabilities were 1.5 (1.3)% and 1.0 (0.5)%, respectively [mean (SD)]. Over 6 weeks, the cyclists then replaced 15 (2)% of their 300 (66) km?·?week^?1 endurance training with 12 HIT sessions, each consisting of six to nine 5-min rides at 80% of ${\dot W}_{\rm peak}$ , separated by a 1-min recovery. HIT increased ${\dot {W}}_{\rm peak}$ from 404 (40) to 424 (53) W (P?40 speeds from 42.0 (3.6) to 43.0 (4.2) km?·?h^?1 (P?40 performances were due to increases in both the absolute work rates from 291 (43) to 327 (51) W (P? ${\dot {W}}_{\rm peak}$ to 78.1 (2.8)% of post-HIT ${\dot {W}}_{\rm peak}$ (P? ${\dot {W}}_{\rm peak}$ (P? ${\dot { W}}_{\rm peak}$ ) work rates. Thus, the ability of the cyclists to sustain higher percentages of ${\dot {W}}_{\rm peak}$ in TT₄₀ performances after HIT was not due to lower rates of CHO oxidation. Higher relative work rates in the TT₄₀ rides following HIT increased the estimated rates of CHO oxidation from ≈?4.3 to ≈?5.1 g?·?min^?1.     

Effects of hypoxic training on normoxic maximal aerobic power output

The responses to 1-leg submaximal and maximal exercise have been studied in four male subjects before and after a 5 week training programme. One leg was trained under normoxic conditions and the other under hypoxic ( \(F_{IO_2 } \) =0.12) conditions for 30 min/day, 3 times/week at a fixed absolute work load which approximated to 75% of the limb's normoxic \(\dot V_{O_2 \max } \) . Before and after training both limbs were measured in normoxia, one limb was additionally measured in hypoxia. The aim of the experiments being to use each subject as his own control and to try and elucidate the effects of hypoxia per se as a training stimulus to the improvement of maximal aerobic power output ( \(\dot V_{O_2 \max } \) ) measured in normoxia. The results showed that before training the responses to exercise at submaximal and maximal levels were identical in each limb; the effects of hypoxia being to raise V _E1.5 and f _H1.5, to reduce \(\dot V_{O_2 \max } \) and to leave \(\dot V_{O_2 450} \) unchanged. The effects of the two types of training were to reduce \(\dot V_{O_2 450} \) , decrease f _H1.5 and increase \(\dot V_{O_2 \max } \) , the effects being independent of the \(F_{IO_2 } \) . The changes in \(\dot V_{O_2 \max } \) of the hypoxic and normoxic trained legs were related to the initial \(\dot V_{O_2 \max } \) of each subjects' limb. It was concluded that our investigation lends no support to the view that hypoxia has either an additive or potentiating effect with exercise during a training programme on the improvement of aerobic power output measured under normoxic conditions.     

Plasma catecholamine concentration during dynamic exercise involving different muscle groups

The change in plasma catecholamine concentration (ΔC) has been studied in four healthy male subjects during work, involving different muscle groups, whilst breathing air and 45% oxygen. The results show that during arm and (1- and 2-) leg(s) work ΔC was more closely associated with relative (expressed as a % of \(\dot V_{{\text{O}}_{{\text{2max}}} }\) ) than absolute work load; a rise in C occurred at ～ 60% \(\dot V_{{\text{O}}_{{\text{2max}}} }\) in all 3 forms of exercise. However, in arm and 1-leg work the curves relating ΔC to % \(\dot V_{{\text{O}}_{{\text{2max}}} }\) were displaced to the right indicating the independence of the two variables. Further, breathing 45% oxygen reduced ΔC but was without effect on either \(\dot V_{O_2 } \) at a given work load or \(\dot V_{{\text{O}}_{{\text{2max}}} }\) . For a given \(\dot V_{O_2 } \) , ΔC was inversely related to the effective muscle (plus bone) volume used to perform the work and associated with change of blood lactic acid (LA) concentration, but again the use of exercise involving different muscle groups indicated that the changes in C and LA were essentially independent. This was also true of the changes of C with cardiac output but not cardiac frequency (f _H ). Plasma C changed as a curvilinear function of f _H , the association between the two variables being independent of type of exercise and inspired O₂ concentration within the range used in this study. This suggests that the rise in C and f _H in exercise may be closely related to circulatory stress and may reflect the degree of vasoconstriction present in ‘non-active’ tissues and efficacy of the body's ability to maintain the integrity of systemic blood pressure in the face of increased demands of the exercising muscles for blood and the transport of oxygen.     

The\dot VCO_2 /\dot VO_2 relationship during heavy,constant work rate exercise reflects the rate of lactic acid accumulation

Oxygen uptake ( $\dot VO_2 $ ) kinetics have been reported to be modified when lactic acid accumulates; however little attention has been given to the simultaneous carbon dioxide production ( $\dot VCO_2 $ >) kinetics. To demonstrate how $\dot VCO_2 $ changes as a function of $\dot VO_2 $ when lactic acid is buffered by bicarbonate, eight healthy subjects performed 6-min constant work rate cycle ergometer exercise tests at moderate, heavy and very heavy exercise intensities. $\dot VCO_2 $ and $\dot VO_2 $ were measured breath-by-breath, and arterial blood samples were obtained every 7.5 s during the first 3 min of exercise, and were analyzed for pH, partial pressure of carbon dioxide, standard bicarbonate, and lactate. $\dot VCO_2 $ abruptly increased relative to $\dot VO_2 $ between 40 and 50 s after the start of exercise for the high exercise intensities. These gas exchange events were observed to correlate well with the time and $\dot VO_2 $ at which lactic acid increased and plasma bicarbonate decreased (r = 0.90,r = 0.95, respectively). We conclude that bicarbonate buffering of lactic acid can be determined from the acceleration of $\dot VCO_2 $ relative to $\dot VO_2 $ kinetics in response to constant work rate exercise and the increase is quantitatively related to the magnitude of the lactic acid increase. This is easily visualized from a plot of $\dot VCO_2 $ as a function of $\dot VO_2 $ .     

Influence of exercise intensity on respiratory muscle fatigue and brachial artery blood flow during cycling exercise

Purpose

During high intensity exercise, both respiratory muscle fatigue and cardiovascular reflexes occur; however, it is not known how inactive limb blood flow is influenced. The purpose of this study was to determine the influence of moderate and high exercise intensity on respiratory muscle fatigue and inactive limb muscle and cutaneous blood flow during exercise.

Methods

Twelve men cycled at 70 and 85 % \(\dot{V}{\text{O}}_{{ 2_{ {\rm max} } }}\) for 20 min. Subjects also performed a second 85 % \(\dot{V}{\text{O}}_{{ 2_{ {\rm max} } }}\) test after ingesting 1,800 mg of N-acetylcysteine (NAC), which has been shown to reduce respiratory muscle fatigue (RMF). Maximum inspiratory pressures (P _Imax), brachial artery blood flow (BABF), cutaneous vascular conductance (CVC), and mean arterial pressure were measured at rest and during exercise.

Results

Significant RMF occurred with 85 % \(\dot{V}{\text{O}}_{{ 2_{ {\rm max} } }}\) (P _Imax, ?12.8 ± 9.8 %), but not with 70 % \(\dot{V}{\text{O}}_{{ 2_{ {\rm max} } }}\) (P _Imax, ?5.0 ± 5.9 %). BABF and BA vascular conductance were significantly lower at end exercise of the 85 % \(\dot{V}{\text{O}}_{{ 2_{ {\rm max} } }}\) test compared to the 70 % \(\dot{V}{\text{O}}_{{ 2_{ {\rm max} } }}\) test. CVC during exercise was not different (p > 0.05) between trials. With NAC, RMF was reduced (p < 0.05) and BABF was significantly higher (~30 %) compared to 85 % \(\dot{V}{\text{O}}_{{ 2_{ {\rm max} } }}\) (p < 0.05).

Conclusions

These data suggest that heavy whole-body exercise at 85 % \(\dot{V}{\text{O}}_{{ 2_{ {\rm max} } }}\) leads to RMF, decreases in inactive arm blood flow, and vascular conductance, but not cutaneous blood flow.     

Central and peripheral adjustments during high-intensity exercise following cold water immersion

Purpose

We investigated the acute effects of cold water immersion (CWI) or passive recovery (PAS) on physiological responses during high-intensity interval training (HIIT).

Methods

In a crossover design, 14 cyclists completed 2 HIIT sessions (HIIT1 and HIIT2) separated by 30 min. Between HIIT sessions, they stood in cold water (10 °C) up to their umbilicus, or at room temperature (27 °C) for 5 min. The natural logarithm of square-root of mean squared differences of successive R–R intervals (ln rMSSD) was assessed pre- and post-HIIT1 and HIIT2. Stroke volume (SV), cardiac output ( $ \dot{Q} $ ), O₂ uptake ( $ \dot{V} $ O₂), total muscle hemoglobin (t _Hb) and oxygenation of the vastus lateralis were recorded (using near infrared spectroscopy); heart rate, $ \dot{Q} $ , and $ \dot{V} $ O₂ on-kinetics (i.e., mean response time, MRT), muscle de-oxygenation rate, and anaerobic contribution to exercise were calculated for HIIT1 and HIIT2.

Results

ln rMSSD was likely higher [between-trial difference (90 % confidence interval) [+13.2 % (3.3; 24.0)] after CWI compared with PAS. CWI also likely increased SV [+5.9 % (?0.1; 12.1)], possibly increased $ \dot{Q} $ [+4.4 % (?1.0; 10.3)], possibly slowed $ \dot{Q} $ MRT [+18.3 % (?4.1; 46.0)], very likely slowed $ \dot{V} $ O₂ MRT [+16.5 % (5.8; 28.4)], and likely increased the anaerobic contribution to exercise [+9.7 % (?1.7; 22.5)].

Conclusion

CWI between HIIT slowed $ \dot{V} $ O₂ on-kinetics, leading to increased anaerobic contribution during HIIT2. This detrimental effect of CWI was likely related to peripheral adjustments, because the slowing of $ \dot{V} $ O₂ on-kinetics was twofold greater than that of central delivery of O₂ (i.e., $ \dot{Q} $ ). CWI has detrimental effects on high-intensity aerobic exercise performance that persist for ≥45 min.     

Untersuchung zur Tagesperiodik verschiedener Kreislauf-und Atemgrößen bei submaximalen und maximalen Leistungen am Fahrradergometer

The maximal aerobic power of six highly trained young cyclist, mean age 16.3 years and mean \(\dot V_{O_2 \max } \) 4.9 l/min, was directly measured at intervals of 4 hrs. A Latin square design was used for the test order. At submaximal work of O₂-consumption 2.4 to 4.4 l/min no circadian variation of any single function was found. However, at maximal work load the differences between the maxima and minima values were 12.4% for maximal work output ( \(\dot W_{\max } \) ), 7.8% for expiratory minute volume ( \(\dot V_{E\max } \) ), 5.7% for maximal aerobic power ( \(\dot V_{O_2 \max } \) ) and 3.4% for maximal heart rate (HR _max). All the functions—with the exception of \(\dot V_{O_2 \max } \) —had their minima at 0300 hrs; the minima of \(\dot V_{O_2 \max } \) was reached already at 2300 hours. The maxima-values of \(\dot V_{E\max } \) and \(\dot V_{O_2 \max } \) were measured at 1500 hrs, of \(\dot W_{\max } \) andHR _max at 0700 and ofHR _rest at 1900 hrs correspondingly. A one-tailed test showed significant differences between the maxima and minima values of all variables (P<0.05). The results suggest a decreased cardiopulmonary working capacity at night. However, this impairment is only of practical importance if the work will be done near the limit of endurance capacity. Besides it will suggest, that the indirect methods for assessing the cardiopulmonary capacity based on \(\dot V_{O_2 \max } \) and \(\dot W_{170} \) are not useful at nighttime, because the presuppositions for these methods are limited of the time of day.     

Energy cost of arm stroke,leg kick,and the whole stroke in competitive swimming styles

In male elite swimmers \(\dot V_{{\text{O}}_{\text{2}} } \) at a given velocity in freestyle and backstroke was on average 1 to 2 l x min^?1 lower as compared with breaststroke and butterfly. Except for breaststroke, swimming with arm strokes only demanded a lower \(\dot V_{{\text{O}}_{\text{2}} } \) at a given submaximal velocity than the whole stroke. In freestyle and backstroke the submaximal \(\dot V_{{\text{O}}_{\text{2}} } \) of leg kick at a given velocity was clearly higher than the whole stroke. The highest velocity during maximal swimming was always attained with the whole stroke, and the lowest with the leg kick, except for breast stroke, where the leg kick was most powerful. At a given submaximal \(\dot V_{{\text{O}}_{\text{2}} } \) , heart rate and \(\dot V_{\text{E}} :\dot V_{{\text{O}}_{\text{2}} } \) tended to be higher during swimming with arm strokes only as compared with the whole stroke. Highest values for \(\dot V_{{\text{O}}_{\text{2}} } \) , heart rate and blood lactate during maximal exercise were almost always attained when swimming the whole stroke, and lowest when swimming with arm strokes only. At higher velocities body drag was 0.5 to 0.9 kp lower when arms or legs were supported by a cork plate as compared with body drag without support.     

Influence of thigh activation on the \dot{V}O2 slow component in boys and men

Purpose

During constant work rate exercise above the lactate threshold (LT), the initial rapid phase of pulmonary oxygen uptake ( \(\dot{V}\) O₂) kinetics is supplemented by an additional \(\dot{V}\) O₂ slow component ( \(\dot{V}\) O_2Sc) which reduces the efficiency of muscular work. The \(\dot{V}\) O_2Sc amplitude has been shown to increase with maturation but the mechanisms are poorly understood. We utilized the transverse relaxation time (T ₂) of muscle protons from magnetic resonance imaging (MRI) to test the hypothesis that a lower \(\dot{V}\) O₂ slow component ( \(\dot{V}\) O_2Sc) amplitude in children would be associated with a reduced muscle recruitment compared to adults.

Methods

Eight boys (mean age 11.4 ± 0.4) and eight men (mean age 25.3 ± 3.3 years) completed repeated step transitions of unloaded-to-very heavy-intensity (U → VH) exercise on a cycle ergometer. MRI scans of the thigh region were acquired at rest and after VH exercise up to the \(\dot{V}\) O_2Sc time delay (ScTD) and after 6 min. T ₂ for each of eight muscles was adjusted in relation to cross-sectional area and then summed to provide the area-weighted ΣT ₂ as an index of thigh recruitment.

Results

There were no child/adult differences in the relative \(\dot{V}\) O_2Sc amplitude [Boys 14 ± 7 vs. Men 18 ± 3 %, P = 0.15, effect size (ES) = 0.8] during which the change (?) in area-weighted ΣT ₂ between the ScTD and 6 min was not different between groups (Boys 1.6 ± 1.2 vs. Men 2.3 ± 1.1 ms, P = 0.27, ES = 0.6). A positive and strong correlation was found between the relative \(\dot{V}\) O_2Sc amplitude and the magnitude of the area-weighted ?ΣT ₂ in men (r = 0.92, P = 0.001) but not in boys (r = 0.09, P = 0.84).

Conclusions

This study provides evidence to show that progressive muscle recruitment (as inferred from T ₂ changes) contributes to the development of the \(\dot{V}\) O_2Sc during intense submaximal exercise independent of age.     

Perceived exertion as a tool to self-regulate exercise in individuals with tetraplegia

The purpose of this investigation was to examine the use of subjective rating of perceived exertion (RPE) as a tool to self-regulate the intensity of wheelchair propulsive exercise in individuals with tetraplegia. Eight motor complete tetraplegic (C5/6 and below; ASIA Impairment Scale = A) participants completed a submaximal incremental exercise test followed by a graded exercise test to exhaustion to determine peak oxygen uptake ( $ \dot{V}O_{{ 2 {\text{peak}}}} $ ) on a wheelchair ergometer. On a separate day, a 20-min exercise bout was completed at an individualised imposed power output (PO) equating to 70 % of $ \dot{V}O_{{ 2 {\text{peak}}}} $ . On a third occasion, participants were instructed to maintain a workload equivalent to the average RPE for the 20-min imposed condition. $ \dot{V}O_{2} $ , heart rate (HR) and PO were measured at 1-min intervals and blood lactate concentration [BLa^?] was measured at 0, 10 and 20 min. No differences (P > 0.17) were found between mean $ \dot{V}O_{2} $ , %  $ \dot{V}O_{{ 2 {\text{peak}}}} $ , HR, % HR_peak, [BLa^?], velocity or PO between the imposed and RPE-regulated trials. No significant (P > 0.05) time-by-trial interaction was present for $ \dot{V}O_{2} $ data. A significant interaction (P < 0.001) for the PO data represented a trend for an increase in PO from 10 min to the end of exercise during the RPE-regulated condition. However, post hoc analysis revealed none of the differences in PO across time were significant (P > 0.05). In conclusion, these findings suggest that RPE can be an effective tool for self-regulating 20 min of wheelchair propulsion in a group of trained participants with tetraplegia who are experienced in wheelchair propulsion.     

Skeletal muscle \dot{V} {\text{O}_2} kinetics from cardio-pulmonary measurements: assessing distortions through O2 transport by means of stochastic work-rate signals and circulatory modelling

During non-steady-state exercise, dynamic changes in pulmonary oxygen uptake ( $\dot{V} {\text{O}_{\text{2pulm}}}$ ) are dissociated from skeletal muscle $ \dot{V} {\text{O}_2}$ ( $\dot{V} {\text{O}_{\text{2musc}}}$ ) by changes in lung and venous O₂ concentrations (CvO₂), and the dynamics and distribution of cardiac output (CO) between active muscle and remaining tissues ( $ \dot{Q}_{\text{rem}}$ ). Algorithms can compensate for fluctuations in lung O₂ stores, but the influences of CO and CvO₂ kinetics complicate estimation of $\dot{V} {\text{O}_{\text{2musc}}}$ from cardio-pulmonary measurements. We developed an algorithm to estimate $\dot{V} {\text{O}_{\text{2musc}}}$ kinetics from $\dot{V} {\text{O}_{\text{2pulm}}}$ and heart rate (HR) during exercise. 17 healthy volunteers (28 ± 7 years; 71 ± 12 kg; 7 females) performed incremental exercise using recumbent cycle ergometry ( $\dot{V} {\text{O}_{\text{2peak}}}$ 52 ± 8 ml min^?1 kg^?1). Participants completed a pseudo-random binary sequence (PRBS) test between 30 and 80 W. $\dot{V} {\text{O}_{\text{2pulm}}}$ and HR were measured, and CO was estimated from HR changes and steady-state stroke volume. $\dot{V} {\text{O}_{\text{2musc}}}$ was derived from a circulatory model and time series analyses, by solving for the unique combination of venous volume and the perfusion of non-exercising tissues that provided close to mono-exponential $\dot{V} {\text{O}_{\text{2musc}}}$ kinetics. Independent simulations showed that this approach recovered the $\dot{V} {\text{O}_{\text{2musc}}}$ time constant (τ) to within 7 % (R ² = 0.976). Estimates during PRBS were venous volume 2.96 ± 0.54 L; $ \dot{Q}_{\text{rem}}$ 3.63 ± 1.61 L min^?1; τHR 27 ± 11 s; τ $\dot{V} {\text{O}_{\text{2musc}}}$ 33 ± 8 s; τ $\dot{V} {\text{O}_{\text{2pulm}}}$ 43 ± 14 s; $\dot{V} {\text{O}_{\text{2pulm}}}$ time delay 19 ± 8 s. The combination of stochastic test signals, time series analyses, and a circulatory model permitted non-invasive estimates of $\dot{V} {\text{O}_{\text{2musc}}}$ kinetics. Large kinetic dissociations exist between muscular and pulmonary $\dot{V} {\text{O}_{\text{2}}}$ during rapid exercise transients.