Effect of prior exercise at different pedalling frequencies on maximal power in humans

Summary The effect of prior submaximal exercise performed at two different pedalling frequencies, 60 and 120 rev · min^–1, on maximal short-term power output (STPO) was investigated in seven male subjects during cycling exercise on an isokinetic cycle ergometer. Exercise of 6-min duration at a power output equivalent to 92 (SD 5)% maximal oxygen uptake , whether performed at a pedalling frequency of 60 or 120 rev · min^–1, reduced maximal STPO generated at 120 rev · min^–1 to a much greater extent than maximal STPO at 60 rev · min^–1. After 6-min submaximal exercise at 60 rev · min^–1 mean reductions in maximal STPO measured at 120 and 60 rev · min^–1 were 27 (SD 11)% and 15 (SD 9)% respectively, and were not significantly different from the reductions after exercise at 120 rev · min^–1, 20 (SD 13)% and 5 (SD 9)%, respectively. In addition, we measured the effect of prior exercise performed at the same absolute external mechanical power output [236 (SD 30)W] with pedalling frequencies of 60 and 120 rev · min^–1, Although the external power output was the same, the leg forces required (absolute as well as expressed as a proportion of the maximal leg force available at the same velocity) were much higher in prior exercise performed at 60 rev · min^–1. Nevertheless, maximal STPO generated at 120 rev · min^–1 was reduced after exercise at 120 rev-min^–1 [20 (SD 13) %,P<0.05] whereas no significant reduction in maximal STPO was found after prior exercise at 60 rev · min^–1. The present findings would suggest that exercise performed at 92 (SD 5)% , whether at 60 or at 120 rev · min^–1, selectively fatigues the faster fatigue-sensitive fibres resulting in a greater reduction in maximal STPO generated at 120 compared to 60 rev · min^–1. The greater fatigue of maximal STPO generated at 120 rev · min^–1 due to exercise performed at a power output of 236 (SD 30)W at 120 rev · min^–1 compared to 60 rev · min^–1 would suggest a relatively greater contribution of fast fatigue-sensitive fibres when higher movement frequencies and hence different muscle shortening velocities are used at this submaximal exercise intensity.     

Neuromuscular fatigue during prolonged pedalling exercise at different pedalling rates

The purpose of this study was to estimate the differences in neuromuscular fatigue among prolonged pedalling exercises performed at different pedalling rates at a given exercise intensity. The integrated electromyogram (iEMG) slope defined by the changes in iEMG as a function of time during exercise was adopted as the measurement for estimating neuromuscular fatigue. The results of this experiment showed that the relationship between pedalling rate and the means of the iEMG slopes for eight subjects was a quadratic curve and the mean value at 70 rpm [1.56 (SD 0.65) V·min^–1] was significantly smaller (P < 0.01) than that at 50 and 60 rpm [2.25 (SD 0.54), and 2.22 (SD 0.68), respectively]. On the other hand, the mean value of oxygen consumption obtained simultaneously showed a tendency to increase linearly with the increase in pedalling rate, and the values at 70 and 80 rpm were significantly higher than those at 40 and 50 rpm. In conclusion, it was demonstrated that the degree of neuromuscular fatigue estimated by the iEMG changes for five periods of prolonged pedalling exercise at a given exercise intensity was different among the different pedalling rates, and that the pedalling rate at which minimal neuromuscular fatigue was obtained was not coincident with the rate at which the minimal oxygen consumption was obtained, but was coincident with the rate which most subjects preferred. These findings would suggest that the reason why most people prefer a relative higher pedalling rate, even though higher oxygen consumption is required, is closely related to the development of neuromuscular fatigue in the working muscles.     

Human muscle power generating capability during cycling at different pedalling rates

The effect of different pedalling rates (40, 60, 80, 100 and 120 rev min-1) on power generating capability, oxygen uptake (O2) and blood lactate concentration [La]b during incremental tests was studied in seven subjects. No significant differences in O2,max were found (mean +/- S.D., 5.31 +/- 0.13 l min-1). The final external power output delivered to the ergometer during incremental tests (PI,max) was not significantly different when cycling at 60, 80 or 100 rev min-1 (366 +/- 5 W). A significant decrease in PI,max of 60 W was observed at 40 and 120 rev min-1 compared with 60 and 100 rev min-1, respectively (P < 0.01). At 120 rev min-1 there was also a pronounced upward shift of the O2-power output (O2-P) relationship. At 50 W O2 between 80 and 100 rev min-1 amounted to +0.43 l min-1 but to +0.87 l min-1 between 100 and 120 rev min-1. The power output corresponding to 2 and 4 mmol l-1 blood lactate concentration (P[La]2 and P[La]4 ) was also significantly lower (> 50 W) at 120 rev min-1 (P < 0.01) while pedalling at 40, 60, 80 and 100 rev min-1 showed no significant difference. The maximal peak power output (PM, max) during 10 s sprints increased with pedalling rate up to 100 rev min-1. Our study indicates that with increasing pedalling rate the reserves in power generating capability increase, as illustrated by the PI,max/PM,max ratio (54.8, 44.8, 38.1, 34.6, 29.2%), the P[La]4/PM,max ratio (50.4, 38.9, 31.0, 27.7, 22.9%) and the P[La]2/PM,max ratio (42.8, 33.5, 25.6, 23.1, 15.6%) increases. Taking into consideration the O2,max, the PI,max and the reserve in power generating capability we concluded that choosing a high pedalling rate when performing high intensity cycling exercise may be beneficial since it provides greater reserve in power generating capability and this may be advantageous to the muscle in terms of resisting fatigue. However, beyond 100 rev min-1 there is a decrease in external power that can be delivered for an given O2 with an associated earlier onset of metabolic acidosis and clearly this will be disadvantageous for sustained high intensity exercise.     

Neuromuscular function during prolonged pedalling exercise at different cadences

AIM: The purpose of the present work was to assess the strategies set by the central nervous system in order to provide the power output required throughout a prolonged (1-h) pedalling exercise performed at different cadences (50 rpm, 110 rpm and the freely chosen cadence). METHODS: Neuromuscular (NM) activity of vastus lateralis, rectus femoris, biceps femoris and gastrocnemius lateralis muscles was studied quantitatively [root-mean square (RMS) and mean power frequency (MPF)] and qualitatively (timing of onset and offset of muscle bursts during crank cycle). RESULTS: The present results showed that increased cadence resulted in earlier muscle activation in crank cycle. The influence of cadence on RMS and MPF depended on the considered muscle and its functional role during pedalling. Timing of onset and offset of muscle bursts was not altered by fatigue throughout the prolonged exercise. In contrast, RMS and MPF of some muscles was found to increase during prolonged exercise. CONCLUSION: In summary, the present study revealed that tonic aspects of the NM activity (RMS, MPF) are altered during prolonged pedalling exercise, while phasic aspects are remained unchanged. These results suggest that the strategies set by the central nervous system in order to provide the power output required by the exercise are held constant throughout the exercise, but that quantitative aspects of the central drive are increased in order to adapt to the progressive occurrence of the NM fatigue.     

Breathing in man during steady-state exercise on the bicycle at two pedalling frequencies, and during treadmill walking.

1. The breathing pattern, that is the changes in tidal volume (VT), and in inspiratory (TI) and expiratory (TE) durations, has been studied as ventilation increases in exercise. 2. Five healthy subjects were studied in steady-state exercise on a bicycle ergometer, breathing air, at two speeds of pedalling and at six different loads. The pattern was recorded for single breaths. Two of the subjects were also studied while walking on a treadmill with four combinations of speed and gradient. 3. In bicycle exercise, as the CO2 output increased mean VT increased, and mean TI and TE decreased, the absolute decrease in TI being small. The pedalling speed did not affect these relationships. 4. Individual breath durations showed no tendency to group around multiples of the period of rotation of the pedals. 5. In treadmill exercise, no clear influence of stride rate on respiratory rate could be found. The pattern was similar to that found in bicycle exercise. Again no grouping could be found. 6. No evidence of an effect of frequency of limb movement on breathing pattern in submaximal exercise has been found. The selection of breathing pattern seems to be unrelated to the nature of the stimulus but closely geared to the metabolic needs of the body.     

The relationship between cadence,pedalling technique and gross efficiency in cycling

Technique and energy saving are two variables often considered as important for performance in cycling and related to each other. Theoretically, excellent pedalling technique should give high gross efficiency (GE). The purpose of the present study was to examine the relationship between pedalling technique and GE. 10 well-trained cyclists were measured for GE, force effectiveness (FE) and dead centre size (DC) at a work rate corresponding to ~75% of VO₂max during level and inclined cycling, seat adjusted forward and backward, at three different cadences around their own freely chosen cadence (FCC) on an ergometer. Within subjects, FE, DC and GE decreased as cadence increased (p < 0.001). A strong relationship between FE and GE was found, which was to great extent explained by FCC. The relationship between cadence and both FE and GE, within and between subjects, was very similar, irrespective of FCC. There was no difference between level and inclined cycling position. The seat adjustments did not affect FE, DC and GE or the relationship between them. Energy expenditure is strongly coupled to cadence, but force effectiveness, as a measure for pedalling technique, is not likely the cause of this relationship. FE, DC and GE are not affected by body orientation or seat adjustments, indicating that these parameters and the relationship between them are robust to coordinative challenges within a range of cadence, body orientation and seat position that is used in regular cycling.     

Human vagal baroreflex sensitivity fluctuates widely and rhythmically at very low frequencies

Arterial pressure fluctuates rhythmically in healthy supine resting humans, who, from all outward appearances, are in a 'steady-state'. Others have asked, If baroreflex mechanisms are functioning normally, how can arterial pressure be so variable? We reanalysed data from nine healthy young adult men and women and tested the hypotheses that during brief periods of observation, human baroreflex sensitivity fluctuates widely and rhythmically. We estimated vagal baroreflex sensitivity with systolic pressure and R–R interval cross-spectra measured over 15 s segments, moved by 2 s steps through 20-min periods of frequency- and tidal volume-controlled breathing. We studied each subject at the same time on three separate days, with fixed protocols that included two physiological states, supine and passive 40 deg upright tilt, before and after β-adrenergic, cholinergic, and angiotensin converting enzyme blockade. Minimum, mean and maximum (± s.d. ) supine control baroreflex sensitivities averaged 5 ± 3, 18 ± 6, and 55 ± 22 ms mmHg⁻¹. In most subjects, moderate ongoing fluctuations of baroreflex sensitivity were punctuated by brief major peaks, yielding frequency distributions that were skewed positively. Fast Fourier transforms indicated that baroreflex sensitivity fluctuations (expressed as percentages of total power) concentrated more in very low, 0.003–0.04 Hz, than ultra low, 0.0–0.003 Hz, frequencies (77 ± 7 versus 11 ± 8%, P ≤ 0.001, rank sum test). Autoregressive centre frequencies averaged 0.012 ± 0.003 Hz. The periodicity of very low frequency baroreflex sensitivity fluctuations was not influenced significantly by upright tilt, or by variations of autonomic drive or angiotensin activity. Our analysis indicates that during ostensibly 'steady-state' conditions, human vagal baroreflex sensitivity fluctuates in a major way, at very low frequencies.     

Stimulation of the rat somatosensory cortex at different frequencies and pulse widths

Functional MRI (fMRI) during electrical somatosensory stimulation of the rat forepaw is a widely used model to investigate the functional organization of the somatosensory cortex or to study the underlying mechanisms of the blood oxygen level-dependent (BOLD) response. In reality, somatosensory stimuli have complex timing relationships and are of long duration. However, by default electrical sensory stimulation seems to be performed at an extremely short pulse width (0.3 ms). As the pulse duration may alter the neuronal response, our aim was to investigate the influence of a much longer stimulus pulse width (10 ms) using BOLD fMRI during electrical forepaw stimulation. The optimal neuronal response was investigated by varying the stimulus frequency at a fixed pulse duration (10 ms) and amplitude (1 mA). In a parallel experiment we measured the neuronal response directly by recording the somatosensory evoked potentials (SEPs). Quantification of the BOLD data revealed a shift in the optimal response frequencies to 8-10 Hz compared with 1 Hz at 0.3 ms. The amplitude of the recorded SEPs decreased with increasing stimulation frequency and did not display any correlation with the BOLD data. Nevertheless, the summated SEPs, which are a measure of the integrated neuronal activity as a function of time, displayed a similar response profile, with a similar maximum as observed by relative BOLD changes. This shift in optimal excitation frequencies might be related to the fact that an increased pulse width of an electrical stimulus alters the nature of the stimulation, generating also sensorimotor instead of merely somatosensory input. This may influence or alter the activated pathways, resulting in a shift in the optimal response profile.     

Oxygen uptake and blood lactate relationship in subjects of vastly different somatotype

Summary The relationship between oxygen uptake and blood lactate was studied in two human, male, non-athletic subjects of similar age and height but of vastly different somatotype. The obese subject, (weight 109 kg; percent of body fat 30) exhibited a lower level of efficiency during work on a motor driven treadmill (12 km/h, grade + 4%) than the lean subject (weight 60 kg; per cent of body fat 14).On leave, until September 1963, from the University of Massachusetts, Amherst, Massachusetts.     

A positron emission tomography study of self-paced finger movements at different frequencies.

Regional cerebral blood flow was measured in six right-handed volunteers using positron emission tomography during tasks involving repetitive self-paced finger tapping at five different frequencies. The contralateral primary sensorimotor cortex, the pre-supplementary motor area and the cingulate motor area showed significant activation during self-paced finger tapping tasks, compared with the resting state. A positive correlation between the regional cerebral blood flow and the movement frequency was found only in the primary sensorimotor cortex. In the pre-supplementary motor area and the cingulate motor area, however, activity increased when the subject employed movement frequencies faster or slower than his own pace. The same tendency was noted with respect to the relative variability of the inter-tapping interval. The results therefore indicate that the activity of the pre-supplementary motor area and the cingulate motor area may well be related to the increased difficulty in motor control rather than to the execution of the movement itself.     

Effect of thickness of isolated papillary muscles on strength of contraction at different frequencies

The maximum strength of contraction developed by strips of papillary muscles of the left ventricle of rats varied inversely with the thickness of the strip. Strips of different thicknesses showed completely different relationships between concentration strength and frequency, if the increase in frequency was gradual. These differences disappeared if the change to a high frequency was sudden. The function of thick fibers was more considerably affected by blocking of glycolysis with monoiodoacetate. The results are in agreement with the view that an increase in thickness of muscles is accompanied by development of hypoxia in the central zones of the muscles through an increase in length of the oxygen diffusion pathway.Presented by Academician V. V. Parin.Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny. Vol. 70, No. 12, pp. 6–9, December, 1970.     

Heart rate and perceptual response to exercise with different pedalling speed in normal subjects and patients

Summary The perceived exertion rating (RPE) scale of Borg was used to investigate the relationship between perceived exertion and pedalling rate. Normal subjects and patients with chronic obstructive lung disease (Cold) were studied in repeated test series. Work load, applied in a random order, varied from 2.5 to 10 mkp/s (patients) and 5 to 20 mkp/s (normals). Pedalling rate varied from 40 to 60, 80, 100 rpm. At constant work load, RPE decreases during increasing pedalling rate. With respect to validity, RPE, showing a closer relationship to work load than to heart rate, seems to reflect perception of physical stress rather than perception of physiological strain.In addition, the results raise the question of standardization of pedalling rate in bicycle ergometry.Preliminary results have been presented at the XXth World Congress of Sports Medicine, Melbourne, 1974     

Continuous estimation of parameters in skin electrical admittance from simultaneous measurements at two different frequencies

The impedance locus plot in the complex plane has been widely used to present data from measurements of the skin electrical properties. This classical method is, however, limited to electrodermal inactive sites, time-consuming when being performed at several frequencies and inconvenient when measuring evoked responses. To overcome these difficulties we have developed a new method to estimate skin electrical admittance parameters (conductance at extrapolated zero frequency G₀, phase angle (π/2)α and ion relaxation time τ) from simultaneous measurements at two different frequencies with a three-electrode lock-in amplifier measuring system. The new method can also be used to investigate the evoked responses of these parameters in psychophysiological research. The theoretical principles of the new technique are presented in the paper, and the instrumentation as well as measuring procedures are described. The results from experiments on frequency and time dependency of skin electrical admittance show that α is relatively constant or shows only moderate changes compared with G₀ and τ, which change in an opposite manner during evoked responses. Changing the DC offset in the excitation voltage from −1000 to 1000 mV had very little effect upon the estimated variables: G₀ and α (<4 per cent), whereas increase of the excitation alternating voltage amplitude gave a substantial increase in G₀ and α, and a corresponding decrease in τ.