Mechanical work and efficiency in ergometer bicycling at aerobic and anaerobic thresholds

Classic and exertional heatstroke

In the past two decades, record-breaking heatwaves have caused an increasing number of heat-related deaths, including heatstroke, globally. Heatstroke is a heat illness characterized by the rapid rise of core body temperature above 40 °C and central nervous system dysfunction. It is categorized as classic when it results from passive exposure to extreme environmental heat and as exertional when it develops during strenuous exercise. Classic heatstroke occurs in epidemic form and contributes to 9-37% of heat-related fatalities during heatwaves. Exertional heatstroke sporadically affects predominantly young and healthy individuals. Under intensive care, mortality reaches 26.5% and 63.2% in exertional and classic heatstroke, respectively. Pathological studies disclose endothelial cell injury, inflammation, widespread thrombosis and bleeding in most organs. Survivors of heatstroke may experience long-term neurological and cardiovascular complications with a persistent risk of death. No specific therapy other than rapid cooling is available. Physiological and morphological factors contribute to the susceptibility to heatstroke. Future research should identify genetic factors that further describe individual heat illness risk and form the basis of precision-based public health response. Prioritizing research towards fundamental mechanism and diagnostic biomarker discovery is crucial for the design of specific management approaches.

An elliptical trainer may render the Wingate all-out test more anaerobic

The purpose of this study was to evaluate the contribution of the 3 main energy pathways during a 30-second elliptical all-out test (EAT) compared with the Wingate all-out test (WAT). Participants were 12 male team sport players (age, 20.3 ± 1.8 years; body mass, 74.8 ± 12.4 kg; height, 176.0 ± 9.10 cm; body fat, 12.1 ± 1.0%). Net energy outputs from the oxidative, phospholytic, and glycolytic energy systems were calculated from oxygen uptake data recorded during 30-second test, the fast component of postexercise oxygen uptake kinetics, and peak blood lactate concentration, respectively. In addition, mechanical power indices were calculated. The main results showed that compared with WAT, EAT was characterized by significantly lower absolute and relative contributions of the oxidative system (16.9 ± 2.5 J vs. 19.8 ± 4.9 J; p ≤ 0.05 and 11.2 ± 1.5% vs. 15.7 ± 3.28%; p ≤ 0.001). In addition, significantly greater absolute and relative contributions of the phospholytic system (66.1 ± 15.8 J vs. 50.7 ± 15.9 J; p ≤ 0.01 and 43.8 ± 6.62% vs. 39.1 ± 6.87%; p ≤ 0.05) and a significantly greater absolute contribution of the glycolytic system (68.6 ± 18.4 J vs. 57.4 ± 13.7 J; p ≤ 0.01) were observed in EAT compared with WAT. Finally, all power indices, except the fatigue index, were significantly greater in EAT than WAT (p ≤ 0.05). Because of the significantly lower aerobic contribution in EAT compared with WAT, elliptical trainers may be a good alternative to cycle ergometers to assess anaerobic performance in athletes involved in whole-body activities.

The energetics of cycling on Earth, Moon and Mars

From 1885, technological improvements, such as the use of special metal alloys and the application of aerodynamics principles, have transformed the bicycle from a human powered heavy transport system to an efficient, often expensive, object used to move not only in our crowded cities, but also in leisure activities and in sports. In this paper, the concepts of mechanical work and efficiency of cycling together with the corresponding metabolic expenditure are discussed. The effects of altitude and aerodynamic improvements on sports performances are also analysed. A section is dedicated to the analysis of the maximal cycling performances. Finally, since during the next decades the return of Man on the Moon and, why not, a mission to Mars can be realistically hypothesised, a section is dedicated to cycling-based facilities, such as man powered short radius centrifuges, to be used to prevent cardiovascular and skeletal muscle deconditioning otherwise occurring during long-term exposure to microgravity.

Determinants of oxygen consumption during exercise on cycle ergometer: the effects of gravity acceleration

The hypothesis that changes in gravity acceleration (a(g)) affect the linear relationships between oxygen consumption VO2 and mechanical power (w ) so that at any w, VO2 increases linearly with a(g) was tested under conditions where the weight of constant-mass legs was let to vary by inducing changes in a(g) in a human centrifuge. The effects of a(g) on the VO2/w relationship were studied on 14 subjects at two pedalling frequencies (f(p), 1.0 and 1.5 Hz), during four work loads on a cycle ergometer (25, 50, 75 and 100 W) and at four a(g) levels (1.0, 1.5, 2.0 and 2.5 times normal gravity). VO2 increased linearly with w. The slope did not differ significantly at various a(g) and f(p), suggesting invariant mechanical efficiency during cycling, independent of f(p) and a(g). Conversely, the y-intercept of the VO2/w relationship, defined as constant b, increased linearly with a(g). Constant b is the sum of resting VO2 plus internal metabolic power (E (i)). Since the former was the same at all investigated a(g), the increase in constant b was entirely due to an increase in E (i). Since the VO2 versus w lines had similar slopes, the changes in E (i) entirely explained the higher VO2 at each w, as a(g) was increased. In conclusion, the effects of a(g) on VO2 are mediated through changes in E (i), and not in w or in resting VO2.

Effect of internal power on muscular efficiency during cycling exercise

The purpose of this study was to investigate the muscular efficiency during cycling exercise under certain total power output (Ptot) or external power output (Pext) experimental conditions that required a large range of pedal rates from 40 to 120 rpm. Muscular efficiency estimated as a ratio of Ptot, which is sum of internal power output (Pint) and Pext, to rate of energy expenditure above a resting level was investigated in two experiments that featured different conditions on a cycle ergometer, which were carried out at the same levels of Ptot (Exp. 1) and Pext (Exp. 2). Each experiment consisted of three exercise tests with three levels of pedal rates (40, 80 and 120 rpm) lasting for 2-3 min of unloaded cycling followed by 4-5 min of loaded cycling. VO2 during unloaded cycling (approximately 430 ml min(-1) for 40 rpm, approximately 640 ml min(-1) for 80 rpm, approximately 1,600 ml min(-1) for 120 rpm) and the Pint (approximately 3 W for 40 rpm, approximately 25 W for 80 rpm, approximately 90 W for 120 rpm) in the two experiments were markedly increased with increasing pedal rates. The highest muscular efficiency was found at 80 rpm in the two experiments, whereas a remarkable reduction (19%) in muscular efficiency obtained at 120 rpm could be attributable to greater O2 cost due to higher levels of Pint accompanying the increased pedal rates. We concluded that muscular efficiency could be affected by the differences in O2 cost and Pint during cycling under the large range of pedal rates employed in this study.

Influence of "living high-training low" on aerobic performance and economy of work in elite athletes

This study tested the effects of "living high-training low" (Hi-Lo) on aerobic performance and economy of work in elite athletes. Forty endurance athletes (cross-country skiers, swimmers, runners) performed 13-18 consecutive days of training at 1,200 m altitude, by sleeping at 1,200 m (LL, n = 20) or in hypoxic rooms with 5-6 nights at 2,500 m followed by 8-12 nights at 3,000-3,500 m (HL, n = 20). The athletes were evaluated before (pre-), one (post-1) and 15 days (post-15) after Hi-Lo. Economy was assessed from two sub-maximal tests, one non-specific (cycling) and one specific (running or swimming). From pre- to post-1: V(O2)max increased both in HL (+ 7.8%, P < 0.01) and in LL (+ 3.3%, P < 0.05), peak power output (PPO) tended to increase more (P=0.06) in HL (+ 4.1%, P < 0.01) than in LL (+ 1.9%). At post-15, V(O2)max has returned to pre-values in both groups, PPO increased more (P < 0.05) in HL (+ 8.3%, P < 0.01) than in LL (+ 3.8%), V(O2) and power at respiratory compensation point (RCP) increased more (P < 0.05) in HL (+ 9.5%, P < 0.01 and + 11.2%, P < 0.01) than in LL (+ 3.2 and + 3.3%). Cycling mechanical efficiency (8-5%) and economy during specific locomotion (7-7%) increased (P < 0.05) in both groups. This study shows that, for a similar increase in V(O2)max HL had a greater increase in PPO than LL. The efficiency of Hi-Lo is also evidenced 15 days later by higher V(O2) and power at RCP. This study emphasizes that during the post-altitude period, economy of work greatly increases in both groups.

Relationships between mechanical power, O(2) consumption, O(2) deficit and high-energy phosphates during calf exercise in humans

Whole-body O(2) uptake ( VO(2)), O(2) deficit and the concentration of high-energy phosphates (determined by (31)P spectroscopy) in human calf muscle were measured during moderate aerobic square-wave exercise of increasing intensity in ten volunteers. Net VO(2) (above resting) increased linearly with mechanical power, yielding a delta efficiency of 13.1%. "Gross" O(2) deficit increased linearly with net VO(2). The fraction of phosphocreatine (PC) split at steady state increased linearly with the mechanical power and with the O(2) deficit. If the [PC] in resting muscle is known, the slope of the regression between PC split and O(2) deficit (in millimoles) yields the P/O(2) ratio. To calculate this, the O(2) deficit was corrected for the amount of O(2) derived from the body stores, as obtained from literature data. The value so obtained, for a resting [PC] of 30 mM was 5.9, consistent with canonical textbook values. Furthermore, the ratio of "true" O(2) deficit to steady-state VO(2) is a measure of the time constant of VO(2) kinetics at work onset at the muscle level: assuming a monoexponential time course without time delays it amounted to about 17 s, close to the value that can be expected in mammalian muscle at 37 degrees C.

Energy system interaction and relative contribution during maximal exercise

There are 3 distinct yet closely integrated processes that operate together to satisfy the energy requirements of muscle. The anaerobic energy system is divided into alactic and lactic components, referring to the processes involved in the splitting of the stored phosphagens, ATP and phosphocreatine (PCr), and the nonaerobic breakdown of carbohydrate to lactic acid through glycolysis. The aerobic energy system refers to the combustion of carbohydrates and fats in the presence of oxygen. The anaerobic pathways are capable of regenerating ATP at high rates yet are limited by the amount of energy that can be released in a single bout of intense exercise. In contrast, the aerobic system has an enormous capacity yet is somewhat hampered in its ability to delivery energy quickly. The focus of this review is on the interaction and relative contribution of the energy systems during single bouts of maximal exercise. A particular emphasis has been placed on the role of the aerobic energy system during high intensity exercise. Attempts to depict the interaction and relative contribution of the energy systems during maximal exercise first appeared in the 1960s and 1970s. While insightful at the time, these representations were based on calculations of anaerobic energy release that now appear questionable. Given repeated reproduction over the years, these early attempts have lead to 2 common misconceptions in the exercise science and coaching professions. First, that the energy systems respond to the demands of intense exercise in an almost sequential manner, and secondly, that the aerobic system responds slowly to these energy demands, thereby playing little role in determining performance over short durations. More recent research suggests that energy is derived from each of the energy-producing pathways during almost all exercise activities. The duration of maximal exercise at which equal contributions are derived from the anaerobic and aerobic energy systems appears to occur between 1 to 2 minutes and most probably around 75 seconds, a time that is considerably earlier than has traditionally been suggested.

Muscle heat production and anaerobic energy turnover during repeated intense dynamic exercise in humans

1. The aim of the present study was to examine muscle heat production, oxygen uptake and anaerobic energy turnover throughout repeated intense exercise to test the hypotheses that (i) energy turnover is reduced when intense exercise is repeated and (ii) anaerobic energy production is diminished throughout repeated intense exercise. 2. Five subjects performed three 3 min intense one-legged knee-extensor exercise bouts (EX1, EX2 and EX3) at a power output of 65 +/- 5 W (mean +/- S.E.M.), separated by 6 min rest periods. Muscle, femoral arterial and venous temperatures were measured continuously during exercise for the determination of muscle heat production. In addition, thigh blood flow was measured and femoral arterial and venous blood were sampled frequently during exercise for the determination of muscle oxygen uptake. Anaerobic energy turnover was estimated as the difference between total energy turnover and aerobic energy turnover. 3. Prior to exercise, the temperature of the quadriceps muscle was passively elevated to 37.02 +/- 0.12 degrees C and it increased 0.97 +/- 0.08 degrees C during EX1, which was higher (P < 0.05) than during EX2 (0.79 +/- 0.05 degrees C) and EX3 (0.77 +/- 0.06 degrees C). In EX1 the rate of muscle heat accumulation was higher (P < 0.05) during the first 120 s compared to EX2 and EX3, whereas the rate of heat release to the blood was greater (P < 0.05) throughout EX2 and EX3 compared to EX1. The rate of heat production, determined as the sum of heat accumulation and release, was the same in EX1, EX2 and EX3, and it increased (P < 0.05) from 86 +/- 8 during the first 15 s to 157 +/- 7 J s(-1) during the last 15 s of EX1. 4. Oxygen extraction was higher during the first 60 s of EX2 and EX3 than in EX 1 and thigh oxygen uptake was elevated (P < 0.05) during the first 120 s of EX2 and throughout EX3 compared to EX1. The anaerobic energy production during the first 105 s of EX2 and 150 s of EX3 was lower (P < 0.05) than in EX1. 5. The present study demonstrates that when intense exercise is repeated muscle heat production is not changed, but muscle aerobic energy turnover is elevated and anaerobic energy production is reduced during the first minutes of exercise.

Total power output generated during dynamic knee extensor exercise at different contraction frequencies

A novel approach has been developed for the quantification of total mechanical power output produced by an isolated, well-defined muscle group during dynamic exercise in humans at different contraction frequencies. The calculation of total power output comprises the external power delivered to the ergometer (i.e., the external power output setting of the ergometer) and the "internal" power generated to overcome inertial and gravitational forces related to movement of the lower limb. Total power output was determined at contraction frequencies of 60 and 100 rpm. At 60 rpm, the internal power was 18+/- 1 W (range: 16-19 W) at external power outputs that ranged between 0 and 50 W. This was less (P<0.05) than the internal power of 33+/-2 W (27-38 W) at 100 rpm at 0-50 W. Moreover, at 100 rpm, internal power was lower (P<0.05) at the higher external power outputs. Pulmonary oxygen uptake was observed to be greater (P<0.05) at 100 than at 60 rpm at comparable total power outputs, suggesting that mechanical efficiency is lower at 100 rpm. Thus a method was developed that allowed accurate determination of the total power output during exercise generated by an isolated muscle group at different contraction frequencies.

Scientific approach to the 1-h cycling world record: a case study

The purpose of this study was to describe the physiological and aerodynamic characteristics and the preparation for a successful attempt to break the 1-h cycling world record. An elite professional road cyclist (30 yr, 188 cm, 81 kg) performed an incremental laboratory test to assess maximal power output (W(max)) and power output (W(OBLA)), estimated speed (V(OBLA)), and heart rate (HR(OBLA)) at the onset of blood lactate accumulation (OBLA). He also completed an incremental velodrome (cycling track) test (VT1), during which V(OBLAVT1) and HR(OBLAVT1) were measured and W(OBLAVT1) was estimated. W(max) was 572 W, W(OBLA) 505 W, V(OBLA) 52.88 km/h, and HR(OBLA) 183 beats/min. V(OBLAVT1), HR(OBLAVT1), and W(OBLAVT1) were 52.7 km/h, 180 beats/min, and 500.6 W, respectively. Drag coefficient and shape coefficient, measured in a wind tunnel, were 0. 244 and 0.65 m(2), respectively. The cyclist set a world record of 53,040 m, with an estimated average power output of 509.5 W. Based on direct laboratory data of the power vs. oxygen uptake relationship for this cyclist, this is slightly higher than the 497. 25 W corresponding to his oxygen uptake at OBLA (5.65 l/min). In conclusion, 1) the 1-h cycling world record is the result of the interaction between physiological and aerodynamic characteristics; and 2) performance in this event can be predicted using mathematical models that integrate the principal performance-determining variables.

Oxygen cost of dynamic leg exercise on a cycle ergometer: effects of gravity acceleration

A model of the metabolic internal power (Eint) during cycling, which includes the gravity acceleration (ag) as a variable, is presented. This model predicts that Eint is minimal in microgravity (0 g; g=9. 81 m s-2), and increases linearly with ag, whence the hypothesis that the oxygen uptake (VO2) during cycling depends on ag. Repeated VO2 measurements during steady-state exercise at 50, 75 and 100 W on the cycle ergometer, performed in space (0 g) and on Earth (1 g) on two subjects, validated the model. VO2 was determined from the time course of decreasing O2 fraction during rebreathing. The gas volume during rebreathing was determined by the dilution principle, using an insoluble inert gas (SF6). Average VO2 for subject 1 at each power was 0.99, 1.21 and 1.52 L min-1 at 1 g (n=3) and 0.91, 1.13 and 1.32 L min-1 at 0 g (n=5). For subject 2 it was 0.90, 1.12 and 1. 42 L min-1 at 1 g, and 0.76, 0.98 and 1.21 L min-1 at 0 g. These values corresponded to those predicted from the model. Although resting VO2 was lower at 0 g than at 1 g, the net (total minus resting) exercise VO2 was still smaller at 0 g than at 1 g. This difference reflects the lower Eint at 0 g.

Effect of beta-blocking agents with and without intrinsic sympathomimetic activity on work efficiency in healthy men

In order to evaluate the effect of beta-blocking agents with and without intrinsic sympathomimetic activity (ISA) on work efficiency in healthy subjects, we studied the haemodynamic and gas exchange parameters, as well as blood lactate concentrations, during a graded maximal bicycle exercise test performed after perorally given propranolol (PRO) and pindolol (PIN) in seven healthy men. The medications (PRO: 80 mg x 2/day, PIN: 10 mg x 2/day, for seven days) were given in a placebo (PLA) controlled, double-blind, randomized, cross-over fashion. Both the drugs reduced heart rate and blood pressure during exercise equally compared with the placebo. The oxygen uptake at submaximal work loads, as well as at the maximum, was constantly and equally reduced by PRO and PIN compared with PLA. The anaerobic threshold was reached at a slightly lower oxygen uptake for both the drugs compared with the placebo (P < 0.05). No significant difference was, however, observed in the work levels at which the ventilatory anaerobic threshold was reached. Moreover, the gross efficiency, i.e. the amount of work performed at a certain energy consumption level (aerobic + anaerobic), was increased by both PRO (26.7 +/- 0.5%, P < 0.02 vs PLA: 24.7 +/- 0.5%) and PIN (26.5 +/- 0.5%, P < 0.05 vs PLA) at a submaximal work load of 240 W. The results indicate that beta-blocking agents propranolol and pindolol slightly and equally reduce maximal work performance, but increase the efficiency of submaximal work in a way that a certain amount of external work can be done with smaller consumption of oxygen. These findings may contribute to the benefit of beta-blocking agents in patients with coronary heart disease.

Anaerobic ATP production and accumulated O2 deficit in cyclists

Anaerobic ATP production in skeletal muscle and the accumulated oxygen deficit (O2D) incurred during an exhaustive cycle bout (duration = 173 +/- 24 s; intensity = 112 +/- 3% VO2peak), were determined in 10 male cyclists (mean +/- SD: VO2peak = 69.8 +/- 4.2 ml.kg-1.min-1). Anaerobic ATP production (mmol.kg-1 d.w.) was determined from changes in lactate, phosphocreatine, ATP, and ADP in vastus lateralis. Muscle buffer value and the activities of glycogen phosphorylase (PHOS), phosphofructokinase and citrate synthase (CS) were also determined. The anaerobic ATP production determined from measured muscle metabolites was 202.7 +/- 46.9 mmol.kg-1 d.w. and was correlated (P < or = 0.05) with muscle buffer value (r = 0.81), PHOS (r = 0.69) and the ratio of PHOS to CS activity (r = 0.77). The O2D was 55.2 +/- 10.3 ml O2 Eq.kg-1, but was not correlated (P > 0.05) with anaerobic ATP production (r = -0.38), buffer value (r = -0.50) or PHOS (r = -0.39). These latter findings could be explained by error in measuring the O2D and/or muscle anaerobic ATP production in well-trained cyclists.

Anaerobic capacity: a maximal anaerobic running test versus the maximal accumulated oxygen deficit

The present investigation evaluates a maximal anaerobic running test (MART) against the maximal accumulated oxygen deficit (MAOD) for the determination of anaerobic capacity. Essentially, this involved comparing 18 male students performing two randomly assigned supramaximal runs to exhaustion on separate days. Post warm-up and 1, 3, and 6 min postexercise capillary blood samples were taken during both tests for plasma blood lactate (BLa) determination. In the MART only, blood ammonia (BNH3) concentration was measured, while capillary blood samples were additionally taken after every second sprint for BLa determination. Anaerobic capacity, measured as oxygen equivalents in the MART protocol, averaged 112.2 +/- 5.2 ml.kg-1.min-1. Oxygen deficit, representing the anaerobic capacity in the MAOD test, was an average of 74.6 +/- 7.3 ml.kg-1. There was a significant correlation between the MART and MAOD (r = .83, p < .001). BLa values obtained over time in the two tests showed no significant difference, nor was there any difference in the peak BLa recorded. Peak BNH3 concentration recorded was significantly increased from resting levels at exhaustion during the MART.

Effect of end-point cadence on the maximal work-time relationship

This study examined the effect of end-point cadence on the parameters of the work-time relationship determined for cycle ergometry. Eight male subjects completed four maximal tests on an electrically-braked cycle ergometer that regulated a constant power output independent of cadence. The power outputs imposed ranged between an average of 259 W and 403 W, whereas the corresponding durations ranged between 139 s and 1691 s. During each test subjects were required to maintain a cadence of 80-90 rpm. Accumulated time to end-point cadences of 70, 60 and 50 rpm were recorded. The four work-time determinations for each of three end-point cadences were used to determine linear relationships between work and time, yielding both a y-intercept, which represents anaerobic work capacity, and a slope, which is termed critical power (CP), for each end-point cadence. There was a significant increase in the y-intercept as end-point cadence decreased from 70 to 60 rpm (F[1,7] = 36.7, p < 0.001) or 70 to 50 rpm (F[1,7] = 80.1, p < 0.001), but not from 60 rpm to 50 rpm (F[1,7] = 3.28, p > 0.05). In contrast, there was no effect of end-point cadence on CP (F[2,14] = 1.89, p < 0.05). These results demonstrate that the end-point cadence selected to terminate tests only affects the y-intercept of the work-time relationship. To control for this effect, the cadence at which each test is terminated should be standardised if determination of anaerobic work capacity, as represented by the y-intercept, is required.

Oxygen cost of internal work during cycling

The energy cost of internal work and its relationships with lower limb mass and pedalling frequency were studied in four male subjects [age 22.2 (SD 1.5) years, body mass 81.0 (SD 5.1) kg, maximal O2 uptake (VO2max) above resting 3.06 (SD 0.4) l.min-1]. The subjects cycled at 40, 60, 80 and 100 rpm and at five different exercise intensities for every pedalling frequency (unloaded condition, UL); the same exercises were repeated after having increased the lower limbs' masses by 40% (loaded condition, L). The exercise intensities were chosen so that the oxygen consumption (VO2) did not exceed 75% of VO2max. For all the subjects and all the conditions, the rate of VO2 above resting increased linearly with the mechanical power (W). The y-intercepts of the linear regressions of VO2 on W, normalised per kilogram of overall lower limbs mass were the same in both UL and L and increased with the 4.165 power of pedalling frequency (fp). These intercepts were taken to represent the metabolic counterpart of the internal power dissipation in cycling; they amounted to 0.78, 0.34, 3.29 and 10.30 W.kg-1 for pedalling frequencies of 40, 60, 80 and 100 rpm respectively. The slope of the regression lines (delta W/delta VO2) represents the delta efficiency of cycle ergometer exercise; this was also affected by fp, ranging, on average, from 22.9% to 32.0%. These data allowed us to obtain a comprehensive description of the effects of fp (per minute), exercise intensity (W, watts) and lower limbs' mass with or without added loads (mL, kg), on VO2 (ml.min-1) during cycling: VO2 = [mL.(4.3.10(-8).fp4.165/0.35)] + (1/[(3.594.10(-5).fp2 - 0.003.fp + 0.326).0.35]).W. The mean percentage error between the VO2 predicted from this equation and the actual value was 12.6%. This equation showed that the fraction of the overall VO2 due to internal work, for a normal 70-kg subject pedalling at 60 rpm and 100 W was of the order of 0.2.

Gross efficiency of muscular work during step exercise at -15 degrees C and 21 degrees C

In an effort to assess the effect of ambient temperature on the gross efficiency (Effg) of step exercise 12 subjects performed a modified step test either at -15 degrees C or 21 degrees C ascending to three different heights (corresponding to light, moderate and heavy work), for 20 min each with a frequency of 18 steps min-1. Heart rate (HR), rectal temperature, skin temperatures and heat flux from skin were continuously measured. Oxygen consumption was measured during the last 5 min of each step height and perceptions of thermal sensation were recorded. The results indicate that, while using conventional clothing adequate in these temperatures, Effg is altered in a contradictory manner. At -15 degrees C Effg increased with increasing work load, whereas at 21 degrees C it decreased when the work load increased. The highest Effg (heavy work at -15 degrees C and light work at 21 degrees C) values are reflected as rather similar rectal temperatures. (37.4-37.7 degrees C) and identical mean skin temperatures (32.8 degrees C) as well as the same (slightly warm) thermal sensation of the legs. At -15 degrees C the lowest Effg in light work was probably due to the need to warm up the muscles. At 21 degrees C, on the contrary, the activation of heat dissipation systems was probably responsible for the lowest Effg in heavy work.

Mechanical work and efficiency in treadmill running at aerobic and anaerobic thresholds

Mechanical work, mechanical power, energy consumption and mechanical efficiency were studied in constant-speed treadmill running of 5 min at seven different exercises around aerobic (AerT) and anaerobic (AnT) thresholds. The true efficiency of concentric (positive) mechanical work and gross efficiency of the whole body in seven male subjects were calculated. The total mechanical work was calculated from film through the translational, potential and rotational energy states as the sum of the changes of all the mechanical energy states in all body segments allowing energy transfer between segments and from energy state to state. The total energy consumption was measured by combining aerobic and anaerobic energy production in resting and working conditions. When the speed of the treadmill was increased from the velocity of 10 km h-1 (2.8 m s-1) to 22 km h-1 (6.1 m s-1), the concentric mechanical work per one step increased from 129 +/- 45 J to 228 +/- 82 J (P less than 0.01). Oxygen consumption increased from 2.22 +/- 0.27 1 min-1 to 4.47 +/- 0.24 1 min-1. The amount of blood lactate increased from 0.94 +/- 0.53 mmol l-1 at the lowest speed to 9.90 +/- 2.89 mmol l-1 at the highest speed (P less than 0.001). The true efficiency of concentric work decreased from 74 +/- 14% to 56 +/- 8% (P less than 0.05). At the speed of the AerT, the economy of running, the vertical rise of different body segments and mechanical efficiency of positive work were high. The highest gross efficiency was found at the running speed between the AerT and AnT.

Differences in cardiorespiratory responses during and after arm crank and cycle exercise

The differences in cardiorespiratory responses were examined during and after intermittent progressive maximal arm-crank and cycle exercise. Arm-crank exercise was performed in a standing position using no torso restraints to maximize the amount of active skeletal muscle mass. Recovery was followed for 16 min. In the tests a variety of ventilatory gas exchange variables, heart rate, the blood pressure, and the arm venous blood lactate concentration were measured in 21 untrained healthy men aged 24-45 years. At equal submaximal external workloads for arm cranking and cycling (50 and 100 W) the respiratory frequency, tidal volume, pulmonary ventilation, oxygen uptake, carbon dioxide output, the respiratory exchange ratio, heart rate, the arm venous blood lactate concentration, and the ventilatory equivalent for oxygen were higher (P less than 0.001) during arm cranking than cycling. The maximal workload for arm cranking was 44% lower than that for cycling (155 +/- 37 vs 277 +/- 39 W, P less than 0.001) associated with significantly (P less than 0.001) lower maximal tidal volume (-20%), oxygen uptake (-22%), carbon dioxide output (-28%), systolic blood pressure (-17%) and oxygen pulse (-22%) but a higher ventilatory equivalent for carbon dioxide (+22%) and arm venous blood lactate concentration (+37%). However, these responses after arm-crank and cycle exercises behaved almost similarly during recovery. The high cardiorespiratory stress induced by arm work should be taken into account when the work stress and work-rest regimens in actual manual tasks are assessed, and when arm work is used for clinical testing, and in physiotherapy particularly for patients with heart or pulmonary diseases.