Voluntary changes in leg cadence modulate arm cadence during simultaneous arm and leg cycling

Although there is some evidence showing that neural coupling plays an important role in regulating coordination between the upper and lower limbs during walking, it is unclear how tightly the upper and lower limbs are linked during rhythmic movements in humans. The present study was conducted to investigate how coupling of both limbs is coordinated during independent rhythmic movement of the upper and lower limbs. Ten subjects performed simultaneous arm and leg cycling (AL cycling) at their preferred cadences without feedback for 10 s, and then were asked to voluntarily change the cadence (increase, decrease, or stop) of arm or leg cycling. Leg cycling cadence was not affected by voluntary changes in arm cadence. By contrast, arm cycling cadence was significantly altered when leg cycling cadence was changed. These results suggest the existence of a predominant lumbocervical influence of leg cycling on arm cycling during AL cycling.     

Corticospinal excitability is lower during rhythmic arm movement than during tonic contraction

Humans perform rhythmic, locomotor movements with the arms and legs every day. Studies using reflexes to probe the functional role of the CNS suggest that spinal circuits are an important part of the neural control system for rhythmic arm cycling and walking. Here, by studying motor-evoked potentials (MEPs) in response to transcranial magnetic stimulation (TMS) of the motor cortex, and H-reflexes induced by electrical stimulation of peripheral nerves, we show a reduction in corticospinal excitability during rhythmic arm movement compared with tonic, voluntary contraction. Responses were compared between arm cycling and tonic contraction at four positions, while participants generated similar levels of muscle activity. Both H-reflexes and MEPs were significantly smaller during arm cycling than during tonic contraction at the midpoint of arm flexion (F = 13.51, P = 0.006; F = 11.83, P = 0.009). Subthreshold TMS significantly facilitated the FCR H-reflex during tonic contractions, but did not significantly modulate H-reflex amplitude during arm cycling. The data indicate a reduction in the responsiveness of cells constituting the fast, monosynaptic, corticospinal pathway during arm cycling and suggest that the motor cortex may contribute less to motor drive during rhythmic arm movement than during tonic, voluntary contraction. Our results are consistent with the idea that subcortical regions contribute to the control of rhythmic arm movements despite highly developed corticospinal projections to the human upper limb.     

Evidence for freely chosen pedalling rate during submaximal cycling to be a robust innate voluntary motor rhythm

Freely chosen pedalling rate during cycling represents a voluntary rhythmic movement. It is unclear to what extent this is influenced by internal (e.g. loading on the cardiopulmonary system) and external (e.g. mechanical loading) conditions. It is also unclear just how robust a voluntary motor rhythm, the freely chosen pedalling rate, actually is. The present study investigated (N = 8) whether or not the freely chosen pedalling rate during submaximal cycling was affected by separate increases in loading on the cardiopulmonary system (changed by exposure to acute simulated altitude of 3,000 m above sea level) and mechanical loading (changed by exposure to increased power output and thereby pedal force). We also investigated (N = 7) whether or not the freely chosen pedalling rate and another voluntary motor rhythm, unimanual unloaded index finger tapping rate, shared common characteristics of steadiness and individuality over a 12-week period. Results showed that the freely chosen pedalling rate was unaffected by increased loading on the cardiopulmonary system at constant mechanical loading, and vice versa. Further, the pedalling rate was steady in the longitudinal perspective (as was the tapping rate), and like tapping rate, pedalling rate was highly individual. In total this indicated that freely chosen pedalling rate primarily is a robust innate voluntary motor rhythm, likely under primary influence of central pattern generators that again are minimally affected by internal and external conditions during submaximal cycling.     

Auditory feedback affects the long-range correlation of isochronous serial interval production: support for a closed-loop or memory model of timing

Long-range dependence is a characteristic property of successively produced time intervals, such as in un-paced or continuation tapping. We hypothesise in the present paper that serial dependence in such tasks could be related to a closed-loop regulation process, in which the current interval is determined by preceding ones. As a consequence, the quality of sensory feedback is likely to affect serial dependence. An experiment with human participants shows that diminished sensory information tends to increase the Hurst exponent for short inter-onset intervals and tends to decrease it for long intervals. A simulation shows that a simple auto-regressive model, whose order depends on the ratio between the inter-onset interval and an assumed temporal integration span, is able to account for most of our empirical results, including the duration specificity of long-range correlation.

Heart rate variability and nonlinear dynamic analysis in patients with stress-induced cardiomyopathy

Complexity-based analyses may quantify abnormalities in heart rate variability (HRV). The aim of this study was to investigate the clinical and prognostic significances of dynamic HRV changes in patients with stress-induced cardiomyopathy Takotsubo syndrome (TS) by means of linear and nonlinear analysis. Patients with TS were included in study after complete noninvasive and invasive cardiovascular diagnostic evaluation and compared to an age and gender matched control group of healthy subjects. Series of R–R interval and of ST–T interval values were obtained from 24-h ECG recordings after digital sampling. HRV analysis was performed by ‘range rescaled analysis’ to determine the Hurst exponent, by detrended fluctuation analysis to quantify fractal long-range correlation properties, and by approximate entropy to assess time-series predictability. Short- and long-term fractal-scaling exponents were significantly higher in patients with TS in acute phases, opposite to lower approximate entropy and Hurst exponent, but all variables normalized in a few weeks. Dynamic HRV analysis allows assessing changes in complexity features of HRV in TS patients during the acute stage, and to monitor recovery after treatment, thus complementing traditional ECG and clinically analysis.     

Discharge rate variability influences the variation in force fluctuations across the working range of a hand muscle

The goal of this study was to improve the ability of a motor unit model to predict experimentally measured force variability across a wide range of forces. Motor unit discharge characteristics were obtained from 38 motor units of the first dorsal interosseus muscle. Motor unit discharges were recorded in separate isometric contractions that ranged from 4 to 85% of the maximal voluntary contraction (MVC) force above recruitment threshold. High-threshold motor units exhibited both greater minimal and peak discharge rates compared with low-threshold units (P < 0.01). Minimal discharge rate increased from 7 to 23 pps, and peak discharge rate increased from 14 to 38 pps with an increase in recruitment threshold. Relative discharge rate variability (CV) decreased exponentially for each motor unit from an average of 30 to 13% as index finger force increased above recruitment threshold. In separate experiments, force variability was assessed at eight force levels from 2 to 95% MVC. The CV for force decreased from 4.9 to 1.4% as force increased from 2 to 15% MVC (P < 0.01) and remained constant at higher forces (1.2-1.9%; P = 0.14). When the motor unit model was revised using these experimental findings, discharge rate variability was the critical factor that resulted in no significant difference between simulated and experimental force variability (P = 0.22) at all force levels. These results support the hypothesis that discharge rate variability is a major determinant of the trends in isometric force variability across the working range of a muscle.     

Effects of swimming with a wet suit on energy expenditure during subsequent cycling.]

The aim of this study was to investigate the effects of swimming with a wetsuit on energy expenditure during subsequent cycling. Nine well-trained triathletes underwent three submaximal trials. The first trial (SC) consisted of a 750-m swim realised at a competition pace, followed by a 10-min cycling exercise at a power output corresponding to the ventilatory threshold . The two other trials were composed of the same cycling exercise, preceded either by a 750-m swim with a wetsuit (WSC) or by a cycling warm-up (Ctrl). The main results are that the WSC trial was characterised by significantly lower swimming cadence (-14%), heart rate (-11%), and lactate values (-47%) compared to the SC trial, p < 0.05. Moreover, cycling efficiency was significantly higher in the WSC trial compared to the SC trial (12.1% difference, p < 0.05). The lower relative intensity observed during swimming with a wetsuit suggest the relative importance of swimming condition on the total performance in a sprint triathlon.     

Factors affecting the increased energy expenditure during passive cycling

Short-duration passive cycling, during which a motor drives the pedals, elevates metabolic energy expenditure. Our purpose was to investigate the feasibility of passive cycling as a physical inactivity countermeasure by quantifying how the number of legs involved, cycling cadence, and habituation influence energy expenditure. Eleven non-cyclists participated. We compared one- and two-leg passive cycling at cadences of 60 and 90 RPM. To investigate if there are habituation effects, we conducted multiple 5-min trials and a prolonged 30-min passive cycling trial. The increase in energy expenditure above rest during passive cycling was significantly greater for two legs compared to one leg (39 vs. 16% at 60 RPM and 96 vs. 45% at 90 RPM). The increase in energy expenditure above rest was greater for 90 versus 60 RPM two-leg passive cycling (96 vs. 39%; p < 0.001). Repeated trials showed no evidence of habituation and the increase in energy expenditure was maintained for the duration of the 30-min trial. In conclusion, energy expenditure during passive cycling is directly related to the number of legs involved and cycling cadence. Two-leg passive cycling at 90 RPM resulted in energy expenditures similar to the walking workstation, suggesting its potential as a physical inactivity countermeasure.     

Fatigue and optimal conditions for short-term work capacity

There is an optimal load and corresponding velocity at which peak power output occurs. It is reasonable to expect that these conditions will change as a result of fatigue during 30 s of all-out cycling. This study evaluated optimal velocity after 30 s of maximal isokinetic cycle ergometer exercise and tested the hypothesis that progressive adjustment of velocity (optimized) during 30 s of all-out cycling would permit greater short-term work capacity (STWC). Non-fatigued optimal cadence [NF_OC, 109.6 (2.5) rpm] was determined for ten males on an SRM ergometer using regression analysis of the torque–angular velocity relation during a 7-s maximal acceleration. Fatigued optimal cadence [73.4 (2.4) rpm] was determined in the same way, immediately after a 30-s isokinetic test at NF_OC. A subsequent trial with cadence decreasing in steps from NF_OC to a conservative estimate of fatigued optimal cadence [83.9 (2.8) rpm] was completed to see if more work could be done with a more optimal cadence during the test. STWC was not different (P=0.50) between the constant [23,681 (764) J] and optimized [23,679 (708) J] conditions. Another more radical progressive change in cadence with four subjects yielded the same result (no increase in STWC). Extraneous factors apparently contribute more to variability in STWC than differences between constant and adjusted optimization of conditions.     

Impaired regulation of stride variability in Parkinson's disease subjects with freezing of gait

Patients with Parkinson's disease (PD) often experience freezing of gait, a debilitating phenomenon during which the subject suddenly becomes unable to start walking or to continue to move forward. Little is known about the gait of those subjects with PD who experience freezing of gait or the pathophysiology of freezing. One possibility is that freezing of gait is a truly paroxysmal phenomenon and that the usual walking pattern of subjects who experience freezing of gait is not different than that of other patients with PD who do not experience these transient episodes of freezing of gait. On the other hand, a recent study noted gait changes just prior to freezing and concluded that dyscontrol of the cadence of walking contributes to freezing. To address this question, we compared the gait of PD subjects with freezing of gait to PD subjects without freezing of gait. Given the potential importance of the dyscontrol of the cadence of walking in freezing, we focused on two aspects of gait dynamics: the average stride time (the inverse of cadence, a measure of the walking pace or rate) and the variability of the stride time (a measure of "dyscontrol," arrhythmicity and unsteadiness). We found that although the average stride time was similar in subjects with and without freezing, stride-to-stride variability was markedly increased among PD subjects with freezing of gait compared to those without freezing of gait, both while "on" (P<0.020) and "off" (P<0.002) anti-parkinsonian medications. Further, we found that increased gait variability was not related to other measures of motor control (while off medications) and levodopa apparently reduced gait variability, both in subjects with and without freezing. These results suggest that a paradigm shift should take place in our view of freezing of gait. PD subjects with freezing of gait have a continuous gait disturbance: the ability to regulate the stride-to-stride variations in gait timing and maintain a stable walking rhythm is markedly impaired in subjects with freezing of gait. In addition, these findings suggest that the inability to control cadence might play an important role in this debilitating phenomenon and highlight the key role of dopamine-mediated pathways in the stride-to-stride regulation of walking. Electronic Publication     

Pedaling time variability is increased in dropped riding position

Variability of cycle-to-cycle duration during a pedaling task is probably related to the rhythmic control of the lower limb muscles as in gait. Although walking variability has been extensively studied for its clinical and physiological implications, pedaling variability has received little attention. The present contribution determines the variability of the cycling time during a 10-min exercise as a function of upper body position. Nine healthy males were required to pedal on cycle-ergometer at a self-selected speed for 10 min in two different upper body positions [hands on upper handlebars (UP) or lower handlebars (DP)]. Time domain measures of cycling variability [total standard deviation (SDtot), mean standard deviation cycle-to-cycle intervals over 100 cycles (SD100), standard deviation of the average cycle-to-cycle intervals over 100 cycles (SDA100)] were measured. Moreover, the same time domain measures were also calculated for heart rate in order to discriminate possible involvements of autonomic regulation. Finally, the structure of the cycle variations has been analyzed in the framework of deterministic chaos calculating the maximum Lyapunov exponents. Significant increases in cycle-to-cycle variability were found for SDtot, SD100 in DP compared to UP, whereas cardiac parameters and other cycling parameters were not changed in the two positions. Moreover, the maximum Lyapunov exponent was significantly more negative in DP. The results suggest that small perturbations of upper body position can influence the control of cycling rhythmicity by increasing the variability in a dissipative deterministic regimen.     

Phase-dependent modulation of soleus H-reflex amplitude induced by rhythmic arm cycling

Rhythmic arm cycling is known to suppress the Hoffmann (H-) reflex amplitudes in the soleus (Sol) muscles of stationary legs. However, it has remained unclear if this suppression is modulated according to the phase of movement in the cycle path or is rather a general setting of excitability level related to rhythmic movement. In the present study we investigated the phase-dependent modulation of the Sol H-reflex induced by rhythmic arm cycling by examining reflex amplitudes at 12 phases of the arm cycle movement. Arm cycling tasks consisted of bilateral, ipsilateral and contralateral movement. Additionally, data were also sampled at 12 static arm positions mimicking those occurring during movement. H-reflexes were evoked and recorded at constant motor wave amplitudes across all conditions. Suppression of Sol H-reflex amplitude was dependent upon the phase of movement (main effect p < 0.0001) during arm cycling, but not during static positioning. Results suggest that locomotor central pattern generators may contribute to the phasic reflex modulation observed in this study. The phasic modulation was more pronounced during bilateral movement, however aspects of the neural control driving this modulation were also present during ipsilateral and contralateral movement.     

Comparison between the rhythmic jaw contractions occurring during sleep and while chewing

The masticatory central pattern generator (CPG) may be implicated in the pathophysiology of sleep bruxism (SB). The aim of this study was to compare rhythmic masticatory muscle activity (RMMA) occurring during sleep related to SB with that of natural voluntary chewing in a sample of sleep bruxers. It was hypothesized that the pace of RMMA during sleep is correlated with the chewing pace. Electromyographic (EMG) surface activity was recorded unilaterally from the masseter muscle of 13 participants diagnosed with SB (mean age ± standard deviation =26.1 ± 9.0 years) by means of portable recorders. For each participant, recordings were carried out in the natural environment setting, always including the dinner time and the entire sleeping period. The time–frequency features of RMMA episodes were extracted automatically offline using a previously validated algorithm. Comparisons between chewing and SB activity indicated that chewing RMMA episodes almost doubled sleep RMMA in duration and power. The mean frequency of SB episodes was 1.0 ± 0.3 Hz, whereas the mean frequency of chewing episodes was 1.5 ± 0.4 Hz. The pace of SB and that of chewing were not correlated significantly (R = ?0.13; P = 0.96). We conclude that sleep RMMA is not related to that of chewing. Despite both activities being accompanied by rhythmic jaw contractions, the pace‐generating mechanism of SB may be independent from that of chewing.     

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.     

Striatal dopaminergic denervation and gait in healthy adults

Parkinsonian-like motor impairments are common in the elderly. The etiology of these symptoms in the absence of clinically diagnosable Parkinson’s disease (PD) is unknown. The aim of this study was to evaluate associations between striatal dopaminergic neuron losses that occur with aging and gait in healthy adults. Forty healthy subjects aged 21–85 years old underwent [¹¹C]-β-CFT dopamine transporter (DAT) positron emission tomography (PET). Subjects were also asked to walk in a gait laboratory at their own pace. Gait variables of interest included average general spatiotemporal characteristics of walking patterns and their standard deviation reflecting gait variability. Segmented nonlinear models were used to investigate the relationship between striatal DAT activity and gait while controlling for age. Gait speed, cadence, and single and double support durations were significantly slower than age-based predictions in adults with lower striatal DAT activity (P < 0.05). After controlling for age, striatal DAT activity was not significantly associated with average step length and step width and with gait variability. We conclude that dopaminergic physiology influences certain aspects of gait independent of age-related changes. The findings of this study may augur novel therapeutic approaches to treating gait disorders in the elderly.     

Accelerometry Reveals Differences in Gait Variability Between Patients with Multiple Sclerosis and Healthy Controls

Variability of movement reflects important information for the maintenance of the health of the system. For pathological populations, changes in variability during gait signal the presence of abnormal motor control strategies. For persons with multiple sclerosis (PwMS), extensive gait problems have been reported including changes in gait variability. While previous studies have focused on footfall variability, the present study used accelerometers on the trunk to measure variability during walking. Thus, the purpose of this study was to examine the variability of the acceleration pattern of the upper and lower trunk in PwMS compared to healthy controls. We extracted linear and nonlinear measures of gait variability from 30 s of steady state walking for 15 PwMS and 15 age-matched healthy controls. PwMS had altered variability compared to controls with greater Lyapunov exponent in the ML (p < 0.001) and AP (p < 0.001) directions, and greater frequency dispersion in the ML direction (p = 0.034). PwMS also demonstrated greater mean velocity in the ML direction (p = 0.045) and lower root mean square of acceleration in the AP direction (p = 0.040). These findings indicate that PwMS have altered structure of variability of the trunk during gait compared to healthy controls and agree with previous findings related to changes in gait variability in PwMS.     

The energetically optimal cadence decreases after prolonged cycling exercise

This study investigated the change in the energetically optimal cadence after prolonged cycling. The energetically optimal cadence (EOC) was determined in 14 experienced cyclists by pulmonary gas exchange at six different cadences (100–50 rpm at 10 rpm intervals). The determination of the EOC was repeated after a prolonged cycling exercise of 55 min duration, where cadence was fixed either at high (>95 rpm) or low (<55 rpm) pedalling rates. The EOC decreased after prolonged cycling exercise at a high as well as at a low fixed cadence (P < 0.01). According to the generalized muscle equations of Hill, this indicates that most likely more type I muscle fibres contribute to muscular power output after fatiguing cycling exercise compared to cycling in the beginning of an exercise bout. We suggest that the determination of EOC might be a potential non-invasive method to detect the qualitative changes in activated muscle fibres, which needs further investigation.     

Nonlinear dynamics of heart rate and oxygen uptake in exhaustive 10,000 m runs: influence of constant vs. freely paced

We hypothesized that a freely paced 10,000 m running race would induce a smaller physiological strain (heart rate and oxygen uptake) compared with one performed at the same average speed but with an imposed constant pace. Furthermore, we analyzed the scaling properties with a wavelet transform algorithm computed log2 (wavelet transform energy) vs. log2 (scale) to get slope alpha, which is the scaling exponent, a measure of the irregularity of a time series. HR was sampled beat by beat and V2O, breath by breath. The enforced constant pace run elicited a significantly higher mean VO2 value (53 +/- 4 vs. 48 +/- 5 ml kg(-1) min(-1), P < 0.001), HR (169 +/- 13 vs. 165 +/- 14 bpm, P < 0.01), and blood lactate concentration (6.6 +/- 0.9 vs. 7.5 +/- 1 mM, P < 0.001) than the freely paced run. HR and VO2 signals showed a scaling behavior, which means that the signals have a similar irregularity (a self-similarity) whatever the scale of analysis may be, in both constant and free-paced 10,000 m runs. The scaling exponent was not significantly different according to the type of run (free vs. constant, P > 0.05) and the signal (HR vs. VO2, P > 0.05). The higher metabolic cost of constant vs. free paced run did not affect the self-similarity of HR and VO2, in either run. The HR signal only kept its scaling behavior only with a distance run, no matter the type of run (free or constant).The results suggest that the larger degree of pace variation in freely paced races may be an intentionally chosen strategy designed to minimize the physiological strain during severe exercise and to prevent a premature termination of effort, even if the variability of the heart rate and VO2, are comparable in an enforced constant vs. a freely paced run and if HR keeps the same variability until the arrival.