Effects of prolonged cycle ergometer exercise on maximal muscle power and oxygen uptake in humans

Summary The mechanical power (W_tot, W·kg^–1) developed during ten revolutions of all-out periods of cycle ergometer exercise (4–9 s) was measured every 5–6 min in six subjects from rest or from a baseline of constant aerobic exercise [50%–80% of maximal oxygen uptake (VO_2max)] of 20–40 min duration. The oxygen uptake [VO₂ (W·kg^–1, 1 ml O₂ = 20.9 J)] and venous blood lactate concentration ([la]_b, mM) were also measured every 15 s and 2 min, respectively. During the first all-out period, W_tot decreased linearly with the intensity of the priming exercise (W_tot = 11.9–0.25·VO₂). After the first all-out period (i greater than 5–6 min), and if the exercise intensity was less than 60% VO_2max, W_tot, VO₂ and [la]_b remained constant until the end of the exercise. For exercise intensities greater than 60% VO_2max, VO₂ and [la]_b showed continuous upward drifts and W_tot continued decreasing. Under these conditions, the rate of decrease of W_tot was linearly related to the rate of increase of V [(d W_tot/dt) (W·kg^–1·s^–1) = 5.0·10^–5 –0.20·(d VO₂/dt) (W·kg^–1·s^–1)] and this was linearly related to the rate of increase of [la]_b [(d VO₂/dt) (W·kg^–1·s^–1) = 2.310^–4 + 5.910^–5·(d [la]_b/dt) (mM·s^–1)]. These findings would suggest that the decrease of W_tot during the first all-out period was due to the decay of phosphocreatine concentration in the exercising muscles occurring at the onset of exercise and the slow drifts of VO₂ (upwards) and of W_tot (downwards) during intense exercise at constant W_tot could be attributed to the continuous accumulation of lactate in the blood (and in the working muscles).     

Influence of two pedalling rate conditions on mechanical output and physiological responses during all-out intermittent exercise

The purpose of this study was to investigate the effect of two cycling velocities on power output and concomitant metabolic and cardiorespiratory responses to repeated all-out exercises. Mean power output (P _m), total work (W _tot), total oxygen consumption (VO_2tot) and blood lactate accumulation (Δ[La]_b) were evaluated in 13 male subjects who performed two series of twelve 5-s bouts of sprint cycling. Recovery periods of 45-s were allowed between trials. One series was executed at optimal velocity (V _opt: velocity for greatest power) and the other one at 50% V _opt (0.5V _opt). Velocities obtained in these conditions were V_opt=116.6 (4.7) rpm; 0.5V_opt=60.6 (4.9) rpm. After a phase of adaptation in oxygen uptake in the first part of the series, the data from the 6th to the 12th sprint were as follows: P _m, 924.6 (73.9) versus 689.2 (61.8) W; W _tot, 29.95 (4.14) versus 22.04 (3.17) kJ; VO_2tot, 12.80 (1.36) versus 10.58 (1.37) l; Δ[La]_b, 2.72 (1.22) versus 0.64 (0.79) mmol.l⁻¹, respectively (P<0.001). Both W _tot and VO_2tot were consistently higher at optimal velocity (+21 and +35.8%, respectively). The present findings demonstrate that during intermittent short-term all-out exercise requiring maximal activation, the energy turnover is not necessarily maximal. It depends on muscle contraction velocity. The increase, lower than expected, in metabolic response from 0.5V _opt to V _opt suggests also that mechanical efficiency is higher at V _opt. Electronic Publication     

Relationship between the increase of effectiveness indexes and the increase of muscular efficiency with cycling power

We determined the index of effectiveness (IE), as defined by the ratio of the tangential (effective force) to the total force applied on the pedals, using a new method proposed by Mornieux et al. (J Biomech, 2005), while simultaneously measuring the muscular efficiency during sub-maximal cycling tests of different intensities. This allowed us to verify whether part of the changes in muscular efficiency could be explained by a better orientation of the force applied on the pedals. Ten subjects were asked to perform an incremental test to exhaustion, starting at 100 W and with 30 W increments every 5 min, at 80 rpm. Gross (GE) and net (NE) efficiencies were calculated from the oxygen uptake and W _Ext measurements. From the three-dimensional force’s measurements, it was possible to measure the total force (F _Tot), including the effective (F _Tang) and ineffective force (F _Rad+Lat). IE has been determined as the ratio between F _Tang and F _Tot, applied on the pedals for three different time intervals, i.e., during the full revolution (IE_360°), the downstroke phase (IE_180°Desc) and the upstroke phase (IE_180°Asc). IE_360° and IE_180°Asc were significantly correlated with GE (r=0.79 and 0.66, respectively) and NE (r=0.66 and 0.99, respectively). In contrast, IE_180°Desc was not correlated to GE or to NE. From a mechanical point of view, during the upstroke, the subject was able to reduce the non-propulsive forces applied by an active muscle contraction, contrary to the downstroke phase. As a consequence, the term ‘passive phase’, which is currently used to characterize the upstroke phase, seems to be obsolete. The IE_180°Asc could also explain small variations of GE and NE for a recreational group.     

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 (P _tot) or external power output (P _ext) experimental conditions that required a large range of pedal rates from 40 to 120 rpm. Muscular efficiency estimated as a ratio of P _tot, which is sum of internal power output (P _int) and P _ext, 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 P _tot (Exp. 1) and P _ext (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. during unloaded cycling (∼430 ml min⁻¹ for 40 rpm, ∼640 ml min⁻¹ for 80 rpm, ∼1,600 ml min⁻¹ for 120 rpm) and the P _int (∼3 W for 40 rpm, ∼25 W for 80 rpm, ∼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 P _int accompanying the increased pedal rates. We concluded that muscular efficiency could be affected by the differences in O₂ cost and P _int during cycling under the large range of pedal rates employed in this study.     

Work and power outputs determined from pedalling and flywheel friction forces during brief maximal exertion on a cycle ergometer

Work and power outputs during short-term, maximal exertion on a friction loaded cycle ergometer are usually calculated from the friction force applied to the flywheel. The inertia of the flywheel is sometimes taken into consideration, but the effects of internal resistances and other factors have been ignored. The purpose of this study was to estimate their effects by comparing work or power output determined from the force exerted on the pedals (pedalling force) with work or power output determined from the friction force and the moment of inertia of the rotational parts. A group of 22 male college students accelerated a cycle ergometer as rapidly as possible for 3 s. The total work output determined from the pedalling force (TW _p) was significantly greater than that calculated from the friction force and the moment of inertia (TW _f). Power output determined from the pedalling force during each pedal stroke (SP_p) was also significantly greater than that calculated from the friction force and the moment of inertia. Percentage difference (%diff), defined by %diff = {(TW _p − TW_f/TW _f} × l00, ranged from 16.8 % to 49.3 % with a mean value of 30.8 (SD 9.1)%. It was observed that %diff values were higher in subjects with greaterTW _p or greater maximalSP _p. These results would indicate that internal resistances and other factors, such as the deformation of the chain and the vibrations of the entire system, may have significant effects on the measurements of work and power outputs. The effects appear to depend on the magnitudes of pedalling force and pedal velocity.     

Influence of cadence,power output and hypoxia on the joint moment distribution during cycling

The purpose of this study was to use a hypoxic stress as a mean to disrupt the normal coordinative pattern during cycling. Seven male cyclists pedalled at three cadence (60, 80, 100 rpm) and three power output (150, 250, 350 W) conditions in normoxia and hypoxia (15% O2). Simultaneous measurements of pedal force, joint kinematics, % oxyhaemoglobin saturation, and minute ventilation were made for each riding condition. A conventional inverse dynamics approach was used to compute the joint moments of force at the hip, knee, and ankle. The relative contribution of the joint moments of force with respect to the total moment was computed for each subject and trial condition. Overall, the ankle contributed on average 21%, the knee 29% and the hip 50% of the total moment. This was not affected by the relative inspired oxygen concentration. Results showed that the relative ankle moment of force remained at 21% regardless of manipulation. The relative hip moment was reduced on average by 4% with increased cadence and increased on average by 4% with increased power output whereas the knee moment responded in the opposite direction. These results suggest that the coordinative pattern in cycling is a dominant characteristic of cycling biomechanics and remains robust even in the face of arterial hypoxemia.     

Effects of active recovery on power output during repeated maximal sprint cycling

The effects of active recovery on metabolic and cardiorespiratory responses and power output were examined during repeated sprints. Male subjects (n = 13) performed two maximal 30-s cycle ergometer sprints, 4 min apart, on two separate occasions with either an active [cycling at 40 (1)% of maximal oxygen uptake; mean (SEM)] or passive recovery. Active recovery resulted in a significantly higher mean power output ( ) during sprint 2, compared with passive recovery [ ] 603 (17) W and 589 (15) W, P < 0.05]. This improvement was totally attributed to a 3.1 (1.0)% higher power generation during the initial 10 s of sprint 2 following the active recovery (P < 0.05), since power output during the last 20 s sprint 2 was the same after both recoveries. Despite the higher power output during sprint 2 after active recovery, no differences were observed between conditions in venous blood lactate and pH, but peak plasma ammonia was significantly higher in the active recovery condition [205 (23) vs 170 (20) μmol · 1⁻¹;P < 0.05]. No differences were found between active and passive recovery in terms of changes in plasma volume or arterial blood pressure throughout the test. However, heart rate between the two 30-s sprints and oxygen uptake during the second sprint were higher for the active compared with passive recovery [148 (3) vs 130 (4) beats · min⁻¹;P < 0.01) and 3.3 (0.1) vs 2.8 (0.1) 1 · min⁻¹;P < 0.01]. These data suggest that recovery of power output during repeated sprint exercise is enhanced when low-intensity exercise is performed between sprints. The beneficial effects of an active recovery are possibly mediated by an increased blood flow to the previously exercised muscle.     

Influence of crank length and crank width on maximal hand cycling power and cadence

The purpose was to compare self-chosen pace during ten repetitions of 60 m running sprints performed on a level surface (SPL), or when running uphill (SPU) or downhill (SPD) on a 4.7% slope. When expressed as percent of maximal running speed for corresponding condition, SPD was lower than SPL (95.28 ± 1.93 vs. 97.31 ± 1.29%; P = 0.044), which was lower than SPU (97.31 ± 1.29 vs. 98.09 ± 0.74%; P = 0.026). Heart rates, blood lactate concentrations and general perceived exertion were lower during SPD (163.8 ± 8.3 bpm, 11.66 ± 1.24 mmol L ⁻¹, and 4.1 ± 1.0) than SPL (169.8 ± 7.8 bpm, 13.69 ± 0.33 mmol L⁻¹, and 5.8 ± 0.6), which were lower than SPU (174.9 ± 8.7 bpm, 15.27 ± 0.02, mmol L⁻¹, and 6.3 ± 0.5) (P < 0.05 for all analyzes). Results show that the level of eccentric muscle loading influences the pacing strategy.     

The effects of various warming up intensities and durations during a short maximal anaerobic exercise

Summary In the literature, few experiments deal with the study of warming up before short exercises. The present paper investigates the influence of different warming up procedures on a short maximal anaerobic exercise leading to exhaustion in 1 min or less.Performance, heart rate, oxygen consumption, and lactic acid level are measured. The performance is improved when light warming up (30% VO₂ max) is used just before the criterion exercise, while it is impaired with a more strenuous warming up (75% VO₂ max). After light warming up, heart rate and oxygen consumption are slightly higher during the criterion exercise as compared with the values without warming up. Warming up itself does not lead to an increase in lactic acid level. When a resting period is introduced between warming up and exercise, no modification of performance occurs whatever the warming up intensity, and no important variation of the physiological measures are observed in this case.     

Neuromuscular function and mechanical efficiency of human leg extensor muscles during jumping exercises

The influence of prestretch amplitude on the mechanical efficiency was examined with 5 subjects, who performed 5 different series of vertical jumps, each of which differed with respect to the mechanics of the knee joint action during the prestretch (eccentric) phase of the contact on the floor. Electromyographic activity was recorded from the major extensor muscles during the entire work period of 1 min per series. In addition, expired air was collected during the test and recovery for determination of energy expenditure. Mechanical work was calculated from the vertical displacement of the body during the jumps. The results indicated that high net efficiency of 38.7% was observed in condition where amplitude of knee bending in eccentric phase was small. In large range motion the corresponding net efficiency was 30.1%. In jumps where no prestretching of extensor muscles ocurred the net efficiency was 19.7%. The high efficiency of small amplitude jumps was characterized by low myoelectrical activity of the leg extensor muscles during the positive (concentric) work phase. In addition, the small amplitude jumps had shorter transition time in the stretch-shortening cycle, high average eccentric force and high stretching speed. Therefore the results suggest that the restitution of elastic energy, which was also related to the length change and stiffness of the muscles during stretch, plays an important role in regulating the mechanical efficiency of work.     

Muscle metabolism during 30, 60 and 90 s of maximal cycling on an air-braked ergometer

Summary This study examined the anaerobic and aerobic contributions to muscle metabolism during high intensity short duration exercise. Six males [mean (SD): age 25.0 (6.0) years, height 179.0 (8.2) cm, mass 70.01 (7.42) kg, 4.63 (0.53) 1 · min^–1, body fat 12.7 (2.3)%] performed three counterbalanced treatments of 30, 60 and 90 s of maximal cycling on an air-braked ergometer. All treatments were also performed on days when biopsies were not taken from the vastus lateralis muscle and cannulae not inserted into a forearm vein to ascertain whether these procedures adversely affected performance. The mean results can be summarised as follows: a Homogenate from vastus lateralis muscle; wm, wet muscle; b biopsies taken from vastus lateralis muscle and cannula inserted into forearm vein; c noninvasive procedures ATP, Adenosine 5-triphosphate; PC, phosphocreatinineThe muscle lactate and O₂ deficit data suggested that 60 and 90 s were more appropriate durations than 30 s for assessing the anaerobic capacity on an air-braked cycle ergometer. The mean power outputs also indicated that the invasive procedures did not adversely affect performance.     

Effects of shortening velocity and of oxygen consumption on efficiency of contraction in dog gastrocnemius

Previous observations have shown that, in isolated perfused dog gastrocnemii in situ, stimulated to aerobic rhythmic isotonic tetanic contractions (at about 40% of maximal isometric force), only about 20% of the overall metabolic power (proportional to the rate of O₂ consumption, O₂) was converted into mechanical power (Ẇ). Here we report that, in the same preparation, the maximal velocity during the shortening phase of each tetanus (v, mm s^–1) increased with the rate of energy dissipation, as given by the difference between O₂ and Ẇ (W kg^–1). The relationship between these variables was described by: v=2.85(O₂–Ẇ)^1.24 (R ²=0.85; n=17). A mathematical analysis of this equation shows that the overall mechanical efficiency (=ẆO₂ ^–1) decreased with increasing v (at constant O₂), whereas it increased with increasing O₂ (at constant v). The net effect of this state of affairs was that the decrease of over the entire range of work intensities was relatively minor (from 0.22 to 0.15), in spite of a large increase of v, (from 40 to 120 mm s^–1), thanks to the concomitant increase of O₂ (from 10 to 25 W kg^–1). So, under these experimental conditions, the energetics of work performance seems to be governed by two conflicting needs. The need for a sufficiently high shortening speed (and hence power output), itself requiring a sufficiently large energy dissipation rate, which, however, brings about a fall in . This is counteracted by the increased O₂, which in turn leads to an increased efficiency at the expense of a fall in shortening speed.This article was published in Human Muscular Function during Dynamic Exercise, Marconnet P, Saltin B, Komi P, Poortmans J (eds) Med Sport Sci 41 (series editors: M. Hebbelink, R.J. Shephard) pp. 1–9, Karger, Basel, 1996. It is reproduced with minor editorial modifications. Permission from Karger is gratefully acknowledged.     

The effects of protective clothing on energy consumption during different activities

Protective clothing (PPC) can have negative effects on worker performance. Currently little is known about the metabolic effects of PPC and previous work has been limited to a few garments and simple walking or stepping. This study investigated the effects of a wide range of PPC on energy consumption during different activities. It is hypothesized that wearing PPC would significantly increase metabolic rate, disproportionally to its weight, during walking, stepping and an obstacle course. Measuring a person’s oxygen consumption during work can give an indirect, but accurate estimate of energy expenditure (metabolic rate). Oxygen consumption was measured during the performance of continuous walking and stepping, and an obstacle course in 14 different PPC ensembles. Increases in perceived exertion and in metabolic rate (2.4–20.9%) when wearing a range of PPC garments compared to a control condition were seen, with increases above 10% being significant (P < 0.05). More than half of the increase could not be attributed to ensemble weight. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. Statement: Energy expenditure is a crucial parameter in the assessment of heat and cold stress, calculation of requirements of food (expeditions, military) and air supplies (SCBA time limits). The observed effect of protective clothing (increases up to 21% in energy use) indicates that neglecting it may put workers at risk in extreme conditions.     

Reproducibility of the exponential rise technique of CO2 rebreathing for measuring P vCO2 and C vCO2 to non-invasively estimate cardiac output during incremental, maximal treadmill exercise

The purpose of this study was to determine the reproducibility of the indirect Fick method for the measurement of mixed venous carbon dioxide partial pressure (P _vCO₂) and venous carbon dioxide content (C _vCO₂) for estimation of cardiac output (Q _c), using the exponential rise method of carbon dioxide rebreathing, during non-steady-state treadmill exercise. Ten healthy participants (eight female and two male) performed three incremental, maximal exercise treadmill tests to exhaustion within 1 week. Non-invasive Q _c measurements were evaluated at rest, during each 3-min stage, and at peak exercise, across three identical treadmill tests, using the exponential rise technique for measuring mixed venous PCO₂ and CCO₂ and estimating venous-arterio carbon dioxide content difference (C _v–aCO₂). Measurements were divided into measured or estimated variables [heart rate (HR), oxygen consumption (V̇O₂), volume of expired carbon dioxide (V̇CO₂), end-tidal carbon dioxide (P _ETCO₂), arterial carbon dioxide partial pressure (P _aCO₂), venous carbon dioxide partial pressure (P _vCO₂), and C _v–aCO₂] and cardiorespiratory variables derived from the measured variables [Q _c, stroke volume (V _s), and arteriovenous oxygen difference (C _a–vO₂)]. In general, the derived cardiorespiratory variables demonstrated acceptable (R=0.61) to high (R>0.80) reproducibility, especially at higher intensities and peak exercise. Measured variables, excluding P _aCO₂ and C _v–aCO₂, also demonstrated acceptable (R=0.6 to 0.79) to high reliability. The current study demonstrated acceptable to high reproducibility of the exponential rise indirect Fick method in measurement of mixed venous PCO₂ and CCO₂ for estimation of Q _c during incremental treadmill exercise testing, especially at high-intensity and peak exercise.     

The mechanical efficiency of locomotion in men and women with special emphasis on stretch-shortening cycle exercises

Summary The mechanical efficiency of the leg extensor musculature of men and women was examined with a special sledge ergometer. The subjects (ten males and ten females) performed (a) pure positive work, (b) pure negative work and (c) a combination of negative and positive work (strech-shortening cycle). The mechanical efficiency of pure positive work was on average 19.8±1.2% for female subjects and 17.4±1.2% for male subjects (t=4.12, P<0.001), although the work intensity was equal in both groups. The mechanical efficiency of pure negative work was slightly lower in women than in men (59.3±14.4% vs 75.6±29.3%). The mechanical efficiency of positive work (₊) in a stretch-shortening cycle exercise was 38.1±6.8% in men and 35.5±6.9% in women. The utilization of prestretch was better for female subjects at low prestretch levels, whereas males showed greater potentiation of elastic energy at higher prestretch levels. Regarding absolute W _el (work due to elasticity) values, male subjects showed greater (P<0.001) values than females (189±44 J vs 115±36 J, respectively). Fundamental differences in neuromuscular functions in men and women might cause the differences in the results obtained.     

The highest intensity and the shortest duration permitting attainment of maximal oxygen uptake during cycling: effects of different methods and aerobic fitness level

The aims of this study were: (1) to verify the validity of previous proposed models to estimate the lowest exercise duration (T _LOW) and the highest intensity (I _HIGH) at which VO₂max is reached (2) to test the hypothesis that parameters involved in these models, and hence the validity of these models are affected by aerobic training status. Thirteen cyclists (EC), eleven runners (ER) and ten untrained (U) subjects performed several cycle-ergometer exercise tests to fatigue in order to determine and estimate T _LOW (ET _LOW) and I _HIGH (EI _HIGH). The relationship between the time to achieved VO₂max and time to exhaustion (T _lim) was used to estimate ET _LOW. EI _HIGH was estimated using the critical power model. I _HIGH was assumed as the highest intensity at which VO₂ was equal or higher than the average of VO₂max values minus one typical error. T _LOW was considered T _lim associated with I _HIGH. No differences were found in T _LOW between ER (170 ± 31 s) and U (209 ± 29 s), however, both showed higher values than EC (117 ± 29 s). I _HIGH was similar between U (269 ± 73 W) and ER (319 ± 50 W), and both were lower than EC (451 ± 33 W). EI _HIGH was similar and significantly correlated with I_HIGH only in U (r = 0.87) and ER (r = 0.62). ET _LOW and T _LOW were different only for U and not significantly correlated in all groups. These data suggest that the aerobic training status affects the validity of the proposed models for estimating I _HIGH.     

Influence of mechanical and metabolic strain on the oxygen consumption slow component during forward pulled running

The possible influence of increased eccentric mechanical work on the increase in oxygen uptake (O₂) after 3 min of running (O₂) was investigated through forward pulled running. Ten subjects ran at individually predetermined constant velocity on a treadmill, while being pulled forward. Ground reaction forces, expired gas and EMGs from leg muscles were collected after 3 min and at the end of the run. O₂ and mechanical work were then calculated. The amplitude of O₂ was 138 (139) ml·min^–1 [mean (SD)]. Increased ventilation explained only 8% of O₂. Stride frequency slightly decreased, inducing a similar decrease in internal work and total mechanical work (all P<0.01), while integrated EMG showed no modifications. It was concluded that O₂ does not come from either an increase in mechanical work production or an increase in muscular activity. O₂ could come from a lower muscle efficiency that could be due to a modification of fibre type recruitment.     

Effect of cycling position on oxygen uptake and preferred cadence in trained cyclists during hill climbing at various power outputs

Numerous researchers have studied the physiological responses to seated and standing cycling, but actual field data are sparse. One open issue is the preferred cadence of trained cyclists while hill climbing. The purpose of this study, therefore, was to examine the affect of cycling position on economy and preferred cadence in trained cyclists while they climbed a moderate grade hill at various power outputs. Eight trained cyclists (25.8 ± 7.2 years, 68.8 ± 5.0 ml kg⁻¹ min⁻¹, peak power 407.6 ± 69.0 W) completed a seated and standing hill climb at approximately 50, 65 and 75% of peak power output (PPO) in the order shown, although cycling position was randomized, i.e., half the cyclists stood or remained seat on their first trial at each power output. Cyclists also performed a maximal trial unrestricted by position. Heart rate, power output, and cadence were measured continuously with a power tap; ventilation , BF and cadence were significantly higher with seated climbing at all intensities; there were no other physiological differences between the climbing positions. These data support the premise that trained cyclists are equally economical using high or low cadences, but may face a limit to benefits gained with increasing cadence.     

Effects of short-term training using SmartCranks on cycle work distribution and power output during cycling

SmartCranks use a free running bearing to promote independent pedal work by each leg during cycling. This system is designed for training the upstroke phase during cycling. The effects of training with SmartCranks on the power output (PO) and on cycle work distribution at the anaerobic threshold and the maximum power level were examined. Twenty male, non-professional cyclists were randomly assigned into intervention and control group, training 5 weeks with SmartCranks and conventional cranks, respectively. Before and after the training period the subjects performed an incremental test to exhaustion. Lactate was measured to determine the individual anaerobic threshold (IAT) and forces at the pedal were recorded to quantify changes in the work distribution over the full revolution. We observed no significant statistical difference for peak power (PO; 333.3 ± 32.8 W vs. 323.3 ± 21.8 W) and PO at IAT (229.6 ± 30.1 W vs. 222.7 ± 25.2 W) for SmartCrank and control conditions, respectively (P > 0.05). However, we did observe that work distribution in the downward phase was significantly reduced in the SmartCranks training group at peak PO (from 70.0 ± 4.9% to 64.3 ± 5.8%; P < 0.05). Although the possible implications of the change in the work distribution of sectors are not known, for the success in cycling performance—indicated by the PO—training with the SmartCranks was not more advantageous than training with conventional bicycle cranks.     

Effects on efficiency in repetitive lifting of load and frequency combinations at a constant total power output

Sumary Boxes were lifted and lowered repetitively at three different combinations of load and frequency. These combinations were chosen such that the total mechanical power generated was constant. Effects of the varying load or frequency conditions (but constant total mechanical power) on the rate of energy expenditure (M) and on the mechanical efficiency (ME) were measured. Mechanical power was determined from film analysis and separated into external power (generated to lift the load) and internal power (to raise the lifter's body mass). The M was determined from oxygen consumption measurements. The ME was calculated in two ways, depending on the definition of mechanical power, including either the external power only (ME_ext) or the total power output (ME_tot). Despite a constant total mechanical power, M increased at higher loads and lower frequencies. This might be explained by the increasing isometric force required in postural and load control. The M increase resulted in a decrease of ME_tot. However, at higher loads and lower frequencies ME_ext increased, indicating that more external work can be done at the same energy costs at higher loads or lower frequencies, which could be of interest from the point of view of occupational physiology. It would seem that at higher loads or lower frequencies the increased costs for isometric muscle action do not outweigh the benefit of raising the body less frequently. Furthermore, it was found that the ME,, in lifting was much lower than the values reported for other kinds of activity. This was due to the large proportion of total power output that was internal power in repetitive lifting [e.g. 83.1% (at a load of 6 kg) in the present study].