A comparison of the effects of mixed static and dynamic work with mainly dynamic work in hot conditions

Current physiological criteria for limiting work in hot conditions are frequently based on responses to mainly dynamic work (eg treadmill walking). Their applicability to industrial situations containing mixed static and dynamic work is questioned, since the physiological responses to static work are different from those of dynamic work. Each of eight subjects attempted a one hour uphill treadmill walk (mainly dynamic work), and an uphill treadmill walk whilst intermittently carrying a 20 kg weight in the arms (mixed static and dynamic work). The external work rates in the two conditions were equal, effected by lowering the treadmill gradient in the loaded condition. Experiments were conducted in a hot climate (33 degrees C dry bulb, 25 degrees C wet bulb). Oxygen consumption, minute ventilation, sweat rate and rated perceived exertion were all significantly higher (p less than 0.001) for the mixed static and dynamic work than for the dynamic work. This was also the case for heart rate and forearm skin temperature (p less than 0.01), and for auditory canal temperature (p less than 0.05). There was no significant difference between the two types of work for mean skin temperature, calf skin temperature and chest skin temperature. These results show that for the same external work, physiological strain and perceived exertion are greater for mixed static and dynamic work (carrying a load in the arms) than for mainly dynamic work (walking on a treadmill). They suggest that it is not appropriate to make direct comparisons of laboratory studies based on dynamic work, with practical situations containing mixed static and dynamic work in the heat.     

Activation of human quadriceps femoris muscle during dynamic contractions: effects of load on fatigue.

Muscle fatigue is both multifactorial and task dependent. Electrical stimulation may assist individuals with paralysis to perform functional activities [functional electrical stimulation (FES), e.g., standing or walking], but muscle fatigue is a limiting factor. One method of optimizing force is to use stimulation patterns that exploit the catchlike property of skeletal muscle [catchlike-inducing trains (CITs)]. Although nonisometric (dynamic) contractions are important parts of both normal physiological activation of skeletal muscles and FES, no previous studies have attempted to identify the effect that the load being lifted by a muscle has on the fatigue produced. This study examined the effects of load on fatigue during dynamic contractions and the augmentation produced by CITs as a function of load. Knee extension in healthy subjects was electrically elicited against three different loads. The highest load produced the least excursion, work, and average power, but it produced the greatest fatigue. CIT augmentation was greatest at the highest load and increased with fatigue. Because CITs were effective during shortening contractions for a variety of loads, they may be of benefit during FES applications.     

Isometric or dynamic training: differential effects on mechanical properties of a human muscle

This work compares the specific effects of 3 mo of moderate, isometric, or dynamic voluntary exercises on the contractile properties of human adductor pollicis muscle. Isometric training consisted of 10 daily contractions of 5-s duration at the frequency of one contraction per minute. Dynamic training consisted of 10 daily series of 10 fast contractions (less than 0.5-s duration) moving a load of one-third of the maximal muscle strength at a frequency of one series per minute. Both training programs produced a concomitant increase in maximal tetanic tension and in peak rate of tension development (Ro). A larger increase (P less than 0.05) was found after isometric training (20 vs. 11% after dynamic exercises), whereas Ro augmented more (P less than 0.05) after dynamic contractions (31 vs. 18% after isometric training). Enhancements of twitch force (Pt), rates of twitch tension development (Rt), and of relaxation (St) were, respectively, 20, 20, and 12% after isometric training. There was no modification of contraction time and time of half relaxation (T 1/2R). Conversely, dynamic training produced increases of Rt (25%) and St (16%), associated with an apparently paradoxical decrease of Pt (10%) and reductions of contraction time (11%) and T 1/2R (9%). Maximal shortening velocity was only increased after dynamic training (21%), whereas the maximal muscle power presented a large increase (P less than 0.05) after isometric exercises (51 vs. 19% after dynamic exercises) and a shift of its optimal peak toward heavier loads. This study suggests that human muscle adapts differently to isometric or to dynamic training programs and provides evidence that its contractile kinetics can be altered by exercises performed in physiological conditions.     

Comparison of global and joint-to-joint methods for estimating the hip joint load and the muscle forces during walking

A three-dimensional musculoskeletal model of the lower limb was developed to study the influence of biarticular muscles on the muscle force distribution and joint loads during walking. A complete walking cycle was recorded for 9 healthy subjects using the standard optoelectronic motion tracking system. Ground contact forces were also measured using a 6-axes force plate. Inverse dynamics was used to compute net joint reactions (forces and torques) in the lower limb. A static optimization method was then used to estimate muscle forces. Two different approaches were used: in the first one named global method, the biarticular muscles exerted a torque on the two joints they spanned at the same time, and in the second one called joint-by-joint method, these biarticular muscles were divided into two mono-articular muscles with geometrical (insertion, origin, via points) and physiological properties remained unchanged. The hip joint load during the gait cycle was then calculated taking into account the effect of muscle contractions. The two approaches resulted in different muscle force repartition: the biarticular muscles were favoured over any set of single-joint muscles with the same physiological function when using the global method. While the two approaches yielded only little difference in the resultant hip load, the examination of muscle power showed that biarticular muscles could produce positive work at one joint and negative work at the other, transferring energy between body segments and thus decreasing the metabolic cost of movement.     

The pattern of changes in physiological parameters in the course of changes in physical exercise intensity

It is well known that metabolic, cardiovascular, and respiratory indices during exercise of moderate intensity are linearly related to the power of the exercise. After the load reaches a definite level, this relationship becomes nonlinear. Different methods for evaluating the intensity of load at which this transition takes place are discussed. The methods for investigating the time course of the transitional process in the systems of energy supply for muscle contractions with the changing intensity of the contractions are described. The dependence of the dynamic characteristics of physiological indices on the fitness level, which, in turn, depends on the age and level of physical activity, is discussed.     

Effect of Resistive Load on the Inspiratory Work and Power of Breathing during Exertion

The resistive work of breathing against an external load during inspiration (WR_I) was measured at the mouth, during sub-maximal exercise in healthy participants. This measure (which excludes the elastic work component) allows the relationship between resistive work and power, ventilation and exercise modality to be explored. A total of 45 adult participants with healthy lung function took part in a series of exercise protocols, in which the relationship between WR_I, power of breathing, PR_I and minute ventilation, were assessed during rest, while treadmill walking or ergometer cycling, over a range of exercise intensities (up to 150 Watts) and ventilation rates (up to 48 L min⁻¹) with applied constant resistive loads of 0.75 and 1.5 kPa.L.sec⁻¹. Resting WR_I was 0.12 JL⁻¹ and PR_I was 0.9 W. At each resistive load, independent of the breathing pattern or exercise mode, the WR_I increased in a linear fashion at 20 mJ per litre of , while PR_I increased exponentially. With increasing resistive load the work and power at any given increased exponentially. Calculation of the power to work ratio during loaded breathing suggests that loads above 1.5 kPa.L.sec⁻¹ make the work of resistive breathing become inhibitive at even a moderate (>30 L sec⁻¹). The relationship between work done and power generated while breathing against resistive loads is independent of the exercise mode (cycling or walking) and that ventilation is limited by the work required to breathe, rather than an inability to maintain or generate power.     

Measurement of activation energy and oxidative phosphorylation onset kinetics in isolated muscle fibers in the absence of cross-bridge cycling

This study utilized N-benzyl-p-toluene sulfonamide (BTS), a potent inhibitor of cross-bridge cycling, to measure 1) the relative metabolic costs of cross-bridge cycling and activation energy during contraction, and 2) oxygen uptake kinetics in the presence and absence of myosin ATPase activity, in isolated Xenopus laevis muscle fibers. Isometric tension development and either cytosolic Ca2+ concentration ([Ca2+]c) or intracellular Po2 (PiO2) were measured during contractions at 20 degrees C in control conditions (Con) and after exposure to 12.5 microM BTS. BTS attenuated tension development to 5+/-0.4% of Con but did not affect either resting or peak [Ca2+]c during repeated isometric contractions. To determine the relative metabolic cost of cross-bridge cycling, we measured the fall in PiO2) (DeltaPiO2; a proxy for Vo2) during contractions in Con and BTS groups. BTS attenuated DeltaP(iO2) by 55+/-6%, reflecting the relative ATP cost of cross-bridge cycling. Thus, extrapolating DeltaPiO2 to a value that would occur at 0% tension suggests that actomyosin ATP requirement is approximately 58% of overall ATP consumption during isometric contractions in mixed fiber types. BTS also slowed the fall in PiO2) (time to 63% of overall DeltaPiO2) from 75+/-9 s (Con) to 101+/-9 s (BTS) (P<0.05), suggesting an important role of the products of ATP hydrolysis in determining the Vo2 onset kinetics. These results demonstrate in isolated skeletal muscle fibers that 1) activation energy accounts for a substantial proportion (approximately 42%) of total ATP cost during isometric contractions, and 2) despite unchanged [Ca2+]c transients, a reduced rate of ATP consumption results in slower Vo2 onset kinetics.     

Characterizing the cost of oviposition in insects: a dynamic model

The development of a consensus model of insect oviposition has been impeded by an unresolved controversy regarding the importance of time costs versus egg costs in mediating the trade-off between current and future reproduction. Here I develop a dynamic optimization model that places time and egg costs in a common currency (opportunity costs expressed as decreased lifetime reproductive success) so that their relative magnitudes can be compared directly. The model incorporates stochasticity in host encounter and mortality risk as well as behavioral plasticity in response to changes in the age and egg load of the ovipositing female. The dynamic model's predictions are congruent with those of a simpler, static model: both time- and egg-mediated costs make important contributions to the overall cost of oviposition. Modest quantitative differences between the costs predicted by the static versus dynamic models show that plasticity of oviposition behavior modulates the opportunity costs incurred by reproducing females. The relative importance of egg-mediated costs increases substantially for oviposition events occurring later in life. I propose that the long debate over how to represent the cost of oviposition should be resolved not by advocating the pre-eminence of one sort of cost above all others, but rather by building models that represent the complementary roles of different costs. In particular, both time and egg costs must be recognized to produce a general model of insect oviposition that incorporates a realistic representation of the cost of reproduction. This revised version was published online in July 2006 with corrections to the Cover Date.     

Determinants of metabolic cost during submaximal cycling.

The metabolic cost of producing submaximal cycling power has been reported to vary with pedaling rate. Pedaling rate, however, governs two physiological phenomena known to influence metabolic cost and efficiency: muscle shortening velocity and the frequency of muscle activation and relaxation. The purpose of this investigation was to determine the relative influence of those two phenomena on metabolic cost during submaximal cycling. Nine trained male cyclists performed submaximal cycling at power outputs intended to elicit 30, 60, and 90% of their individual lactate threshold at four pedaling rates (40, 60, 80, 100 rpm) with three different crank lengths (145, 170, and 195 mm). The combination of four pedaling rates and three crank lengths produced 12 pedal speeds ranging from 0.61 to 2.04 m/s. Metabolic cost was determined by indirect calorimetery, and power output and pedaling rate were recorded. A stepwise multiple linear regression procedure selected mechanical power output, pedal speed, and pedal speed squared as the main determinants of metabolic cost (R(2) = 0.99 +/- 0.01). Neither pedaling rate nor crank length significantly contributed to the regression model. The cost of unloaded cycling and delta efficiency were 150 metabolic watts and 24.7%, respectively, when data from all crank lengths and pedal speeds were included in a regression. Those values increased with increasing pedal speed and ranged from a low of 73 +/- 7 metabolic watts and 22.1 +/- 0.3% (145-mm cranks, 40 rpm) to a high of 297 +/- 23 metabolic watts and 26.6 +/- 0.7% (195-mm cranks, 100 rpm). These results suggest that mechanical power output and pedal speed, a marker for muscle shortening velocity, are the main determinants of metabolic cost during submaximal cycling, whereas pedaling rate (i.e., activation-relaxation rate) does not significantly contribute to metabolic cost.     

Estimation of oxygen cost of internal power during cycling exercise with changing pedal rate

It has been reported that oxygen uptake (VO2) increases exponentially with levels of the pedal rate during cycling. The purpose of this study was therefore to test the hypothesis that the O2 cost for internal power output (Pint) exerted in exercising muscle itself would be larger than for an external power output (Pext) calculated from external load and pedal rate during cycling exercise under various conditions of Pint and Pext in a large range of pedal rates. The O2 cost (DeltaVO2/ Deltapower output) was investigated in three experiments that featured different conditions on a cycle ergometer that were carried out at the same levels of total power output (Ptot; sum of Pint and Pext) (Exp. 1), Pext (Exp. 2) and load (Exp. 3). Each experiment consisted of three exercise tests with three levels of pedal rate (40 rpm for a lower pedal rate: LP; 70-80 rpm for a moderate pedal rate: MP; and 100-120 rpm for a higher pedal rate: HP) lasting for 2-3 min of unloaded cycling followed by 4-5 min of loaded cycling. Blood lactate accumulations (2.3-3.4 mmol l(-1)) at the HP were significantly higher compared with the LP (0.6-0.9 mmol l(-1)) and MP (0.9-1.0 mmol l(-1)) except for the LP in Exp. 1. The VO2 (360-432 ml min(-1) for LP, 479-644 ml min(-1) for MP, 960-1602 ml min(-1) for HP) during unloaded cycling in the three experiments increased exponentially with increasing pedal rates regardless of Pext=0. Moreover, the slope of the VO2-Pint (13.7 ml min(-1) W(-1)) relation revealed a steeper inclination than that of the VO2-Pext (10.2 ml min(-1) W(-1)) relation. We concluded that the O2 cost for Pint was larger than for Pext during the cycling exercises, indicating that the O2 cost for Ptot could be affected by the ratio of Pint to Ptot due to the levels of pedal rate.     

Relationship between hypercapnic and hypoxic stimuli of respiration during muscular activity]

Pulmonary ventilation (V) and alveolar gas composition (PACO2, PAO2) were studied in 12 healthy men who performed gradual muscular work under conditions of controlled hypercapnia, hypoxia, hyperoxia or their combinations. The respiratory response was estimated by absolute values of ventilation at the given PACO2 value and by its rise by 1 mm Hg of increased PACO2 (delta V/delta PACO2) under rest and under transitional and steady-state exercise. The exercise on-switch was accompanied by displacement to the top and an increased slope of the response curve (delta V/delta PACO2) not related to the work load. These changes suggest multiplicative interaction of the neurogenic and hypercapnic drives in the load switch-on. During steady-state exercise an important role of the hypoxic drive was revealed: hypoxemia induced a shift of the delta V/delta PACO2 response curve to a higher level, especially with the great work load. Thus the positive interaction between the hypercapnic and hypoxic respiratory drive augments with muscular exercise.     

Human muscle function following prolonged eccentric exercise

4 subjects performed repeated eccentric contractions with leg extensors during prolonged downhill walking (-25% gradient) at 6.44 km.h-1 until collapse due to muscle weakness (range of exercise duration 29 to 40 min). During the exercise oxygen uptake rose progressively from approximately 45% of the previously determined VO2max at 10 min to approximately 65% at the end of the exercise. Following the exercise there was an immediate, significant, and sustained reduction in maximal voluntary isometric contraction, and short term (anaerobic) power output measured concentrically on an isokinetic ergometer. These reductions in muscle function persisted for 96 hours post exercise, and were reflected by significant reductions in the tension generated at low frequency (20 Hz) relative to higher frequency (50 Hz) percutaneous stimulation of the quadriceps. All four subjects showed an increase in plasma levels of creatine kinase post eccentric exercise. Performing concentric contractions by walking uphill for one hour at a significantly greater metabolic cost failed to induce comparable reductions in muscle function. These results provide evidence for the consequences of prolonged eccentric work upon dynamic function which complements earlier reports of structural, enzymatic, and static function changes.     

Effect of aging on ventilatory response to exercise and CO2

Studies were performed to determine the effects of aging on the ventilatory responsiveness to two known respiratory stimulants, inhaled CO2 and exercise. Although explanation of the physiological mechanisms underlying development of exercise hyperpnea remains elusive, there is much circumstantial evidence that during exercise, however mediated, ventilation is coupled to CO2 production. Thus matched groups of young and elderly subjects were studied to determine the relationship between increasing ventilation and increasing CO2 production (VCO2) during steady-state exercise and the change in their minute ventilation in response to progressive hypercapnia during CO2 rebreathing. We found that the slope of the ventilatory response to hypercapnia was depressed in elderly subjects when compared with the younger control group (delta VE/delta PCO2 = 1.64 +/- 0.21 vs. 2.44 +/- 0.40 l X min-1 X mmHg-1, means +/- SE, respectively). In contrast, the slope of the relationship between ventilation and CO2 production during exercise in the elderly was greater than that of younger subjects (delta VE/delta VCO2 = 29.7 +/- 1.19 vs. 25.3 +/- 1.54, means +/- SE, respectively), as was minute ventilation at a single work load (50 W) (32.4 +/- 2.3 vs. 25.7 +/- 1.54 l/min, means +/- SE, respectively). This increased ventilation during exercise in the elderly was not produced by arterial O2 desaturation, and increased anaerobiasis did not play a role. Instead, the increased ventilation during exercise seems to compensate for increased inefficiency of gas exchange such that exercise remains essentially isocapnic. In conclusion, in the elderly the ventilatory response to hypercapnia is less than in young subjects, whereas the ventilatory response to exercise is greater.     

The short-time Fourier transform and muscle fatigue assessment in dynamic contractions

The mean frequency of the power spectrum of an electromyographic signal is an accepted index for monitoring fatigue in static contractions. There is however, indication that it may be a useful index even in dynamic contractions in which muscle length and/or force may vary. The objective of this investigation was to explore this possibility. An examination of the effects of amplitude modulation on modeled electromyographic signals revealed that changes in variance created in this way do not sufficiently affect characteristic frequency data to obscure a trend with fatigue. This validated the contention that not all non-stationarities in signals necessarily manifest in power spectral parameters. While an investigation of the nature and effects of non-stationarities in real electromyographic signals produced from dynamic contractions indicated that a more complex model is warranted, the results also indicated that averaging associated with estimating spectral parameters with the short-time Fourier transform can control the effects of the more complex non-stationarities. Finally, a fatigue test involving dynamic contractions at a force level under 30% of peak voluntary dynamic range, validated that it was possible to track fatigue in dynamic contractions using a traditional short-time Fourier transform methodology.     

An estimation of the influence of force decrease on the mean power spectral frequency shift of the EMG during repetitive maximum dynamic knee extensions.

Frequency analysis of myoelectric (ME) signals, using the mean power spectral frequency (MNF), has been widely used to characterize peripheral muscle fatigue during isometric contractions assuming constant force. However, during repetitive isokinetic contractions performed with maximum effort, output (force or torque) will decrease markedly during the initial 40-60 contractions, followed by a phase with little or no change. MNF shows a similar pattern. In situations where there exist a significant relationship between MNF and output, part of the decrease in MNF may per se be related to the decrease in force during dynamic contractions. This study estimated force effects on the MNF shifts during repetitive dynamic knee extensions. Twenty healthy volunteers participated in the study and both surface ME signals (from the right vastus lateralis, vastus medialis, and rectus femoris muscles) and the biomechanical signals (force, position, and velocity) of an isokinetic dynamometer were measured. Two tests were performed: (i) 100 repetitive maximum isokinetic contractions of the right knee extensors, and (ii) five gradually increasing static knee extensions before and after (i). The corresponding ME signal time-frequency representations were calculated using the continuous wavelet transform. Compensation of the MNF variables of the repetitive contractions was performed with respect to the individual MNF-force relation based on an average of five gradually increasing contractions. Whether or not compensation was necessary was based on the shape of the MNF-force relationship. A significant compensation of the MNF was found for the repetitive isokinetic contractions. In conclusion, when investigating maximum dynamic contractions, decreases in MNF can be due to mechanisms similar to those found during sustained static contractions (force-independent component of fatigue) and in some subjects due to a direct effect of the change in force (force-dependent component of fatigue). In order to compare MNF shifts during sustained static and repetitive dynamic contractions it is necessary to estimate the force-dependent component of fatigue of dynamic contractions. Our results are preliminary and have to be confirmed in larger experiments using single dynamic contractions when determining the MNF-force relationship of the unfatigued situation.     

Time course of the effects of static stretching on cycling economy

Stretching has been implemented as part of the warm-up before physical events and widely thought to promote increased sport performance and decreased injury risk. However, recent research has concluded that static stretching before many exercises inhibits acute power, strength, and sprinting performance. There is little research examining the time course of these effects on moderate intensity cycling. The purpose of this study was to examine the time course of static stretching on cycling economy. The subjects consisted of 5 men and 5 women highly trained endurance cyclists. The first of 3 visits was baseline testing of their cycling VO2max. The second and third visits were either stretching or no stretching before a 30-minute stationary ride at 65% of their VO2max. The stretching condition consisted of four 30-second repetitions of 5 stretches with an average total stretching time of 16 minutes. VO2 demonstrated a significant condition by time interaction with the 5-minute time point being significantly less in the nonstretching condition (32.66 ± 5.35 ml·kg(-1)·min(-1)) than stretching (34.39 ± 5.39 ml·kg(-1)·min(-1)). No other time points were different. Our results demonstrate that static stretching yielded an acute increase in submaximal VO2; therefore, coaches and highly trained endurance cyclists should exclude static stretching immediately before moderate intensity cycling because it reduces acute cycling economy.     

Intramuscular pressure and EMG relate during static contractions but dissociate with movement and fatigue.

Intramuscular pressure (IMP) and electromyography (EMG) mirror muscle force in the nonfatigued muscle during static contractions. The present study explores whether the constant IMP-EMG relationship with increased force may be extended to dynamic contractions and to fatigued muscle. IMP and EMG were recorded from shoulder muscles in three sessions: 1). brief static arm abductions at angles from 0 to 90 degrees, with and without 1 kg in the hands; 2). dynamic arm abductions at angular velocities from 9 to 90 degrees /s, with and without 1 kg in the hands; and 3). prolonged static arm abduction at 30 degrees for 30 min followed by recovery. IMP and EMG increased in parallel with increasing shoulder torque during brief static tasks. During dynamic contractions, peak IMP and EMG increased to values higher than those during static contractions, and EMG, but not IMP, increased significantly with speed of abduction. In the nonfatigued supraspinatus muscle, a linear relationship was found between IMP and EMG; in contrast, during fatigue and recovery, significant timewise changes of the IMP-to-EMG ratio occurred. The results indicate that IMP should be included along with EMG when mechanical load sharing between muscles is evaluated during dynamic and fatiguing contractions.     

Intrinsic uncoupling of mitochondrial proton pumps. 1. Non-ohmic conductance cannot account for the nonlinear dependence of static head respiration on delta microH

The passive membrane conductance LH1 of rat liver mitochondria has been measured and compared with the quantity nJesh/delta microHsh (n = H+/e stoichiometry; Jesh = rate of electron transfer in static head) over a delta microH range. The two curves approach each other only in the lower part of the range, while they sharply diverge at large values of delta microH. Thus nJesh/delta microHsh cannot be considered to be a measure of LH1 in the upper delta microH region. Only a fraction of the static head electron flow is accounted for by futile proton cycling via leaks. Contaminating open membrane fragments or completely leaky mitochondria can be responsible for only a small part of the residual rate of oxygen consumption. We conclude that a large part of static head respiration must have yet another cause and propose it to be intrinsic uncoupling of the respiratory chain enzymes.     

Physiological Correlates of Emotion-Regulation During Prolonged Cycling Performance

We proposed that experiencing unpleasant emotions during performance represents unsuccessful emotion-regulatory efforts, and that such effort concurrently tax physiological resources. We used data from 2-h cycling trials (N = 28) at a power output equivalent to lactate threshold. Emotions were calculated before and during cycling with ongoing assessments of ventilation, respiratory quotient, heart rate, and oxygen uptake. Emotion data indicated significant changes over time with all participants reporting decreases in vigour and increases in fatigue, with 14 cases of concurrent increases in anger, depression, and tension. After grouping participants into positive and negative emotion groups, a time x unpleasant emotion group ANOVA indicated a significant interaction effect for changes in ventilation (F _6,21 = 3.09, P = .03, Partial Eta² = .47) over time, with no significant difference in other physiological variables or perceived exertion. Among athletes reporting negative emotions, ventilation increased during the middle section, whereas among athletes reporting positive emotions, ventilation increased shortly before completion. Findings suggest that regulating negative emotion is an effortful process taxing physiological substrates.     

Metabolic responses to light arm and leg exercise when sitting

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 VO2 above 0.45 1 X 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 VCO2 (VE/VCO2) gradually decreased during both types of exercise. The ventilatory equivalent for VO2(VE/VO2) 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 1100 ml. 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.