Comparing continuous and intermittent exercise. An "isoeffort" and "isotime" approach

The present study proposes an alternative way of comparing performance and acute physiological responses to continuous exercise with those of intermittent exercise, ensuring similar between-protocol overall effort (isoeffort) and the same total duration of exercise (isotime). This approach was expected to overcome some drawbacks of traditional methods of comparison. Fourteen competitive cyclists (20±3 yrs) performed a preliminary incremental test and four experimental 30-min self-paced protocols, i.e. one continuous and three passive-recovery intermittent exercise protocols with different workto- rest ratios (2 = 40:20s, 1 = 30:30s and 0.5 = 20:40s). A "maximal session effort" prescription was adopted for this experimental design. As expected, a robust perceived exertion template was observed irrespective of exercise protocol. Similar between-protocol pacing strategies further support the use of the proposed approach in competitive cyclists. Total work, oxygen uptake and heart rate mean values were significantly higher (P<0.05) in the continuous compared to intermittent protocols, while lactate values were lower. Manipulating the work-to-rest ratio in intermittent exercise, total work, oxygen uptake and heart rate mean values decreased with the decrease in the work-to-rest ratio, while lactate values increased. Despite this complex physiological picture, all protocols showed similar ventilatory responses and a nearly perfect relationship between respiratory frequency and perceived exertion. In conclusion, our data indicate that overall effort and total duration of exercise are two critical parameters that should both be controlled when comparing continuous with intermittent exercise. On an isoeffort and isotime basis, the work-to-rest ratio manipulation affects physiological responses in a different way from what has been reported in literature with traditional methods of comparison. Finally, our data suggest that during intermittent exercise respiratory frequency reflects physiological strain better than oxygen uptake, heart rate and blood lactate

Motor control during ramp and steady-state muscular efforts investigated by means of sEMG

Several parameters extracted from the EMG, either by linear or non-linear analysis, have been investigated during ramp or steady state muscularefforts. Temporal and frequency parameters have shown a good reliability in describing the kind of neuromuscular control necessary for slow ramps, whereas they were less reliable in describend the quickest ramps. The non-linear parameter, expecially the percentage of determinism (%DET) showed a meaningful behavior connceted to muscular fatigue and motor units (MUs) synchronization

Reproducibility of muscle fibre conduction velocity during linearly increasing force contractions

Muscle fibre conduction velocity (MFCV) is a basic physiological parameter biophysically related to the diameter of muscle fibres and properties of the sarcolemma. The aim of this study was to assess the intersession reproducibility of the relation between voluntary force and estimates of average muscle fibre conduction velocity (MFCV) from multichannel high-density surface electromyographic recordings (HDsEMG). Ten healthy men performed six linearly increasing isometric ankle dorsiflexions on two separate experimental sessions, 4 weeks apart. Each session involved the recordings of voluntary force during maximal isometric (MViF) and submaximal ramp contractions at 35\u201350\u201370% of MViF. Concurrently, the HDsEMG activity was detected from the tibialis anterior muscle and MFCV estimates were derived in 250-ms epochs. Absolute and relative reproducibility of MFCV initial value (intercept) and rate of change (regression slope) as a function of force were assessed by within-subject coefficient of correlation (CVw) and with intraclass correlation coefficient (ICC). MFCV was positively correlated with voluntary force (R2 = 0.75 \ub1 0.12) in all individuals and test conditions (P < 0.001). Average CVw for MFCV intercept and slope were of 2.6 \ub1 2.0% and 11.9 \ub1 3.2% and ICC values of 0.96 and 0.94, respectively. Overall, MFCV regression coefficients showed a high degree of intersession reproducibility in both absolute and relative terms. These results may have important practical implications in the tracking of training-induced neuromuscular changes and/or in the monitoring of the progress of neuromuscular disorders when a full sEMG signal decomposition is problematic or not possible

Whole-body vibrations exposure while walking in place

The human body is exposed to vibration while walking on manufacturing platforms or in transports. In order to minimize the risk of pathologies, anti-vibration equipment can be designed to limit the vibration transmitted to specific body segments. Prevention strategies have been developed starting from the vibration transmissibility and from the apparent mass of standing subjects. Little have been done for the optimization of anti-vibration devices for walking workers. Our work aims at investigating the response of the human body while walking in place. For this purpose, a dedicated experimental procedure involving seven participants walking in place over a vibrating platform has been developed. Participants were exposed to harmonic excitation with six different frequencies (5, 10, 15, 20, 25, and 30 Hz), with an amplitude of 2 m.s−2. The inertial force exerted by the walking subjects exposed to the stimulus was measured by four load cells supporting the platform. Simultaneously, tridimensional acceleration signals were collected at the participant right shank, low-back, and mouth. Vibration transmissibility as well as apparent mass were computed as a function of the excitation frequency. Results indicated a higher transmissibility of the vibration at 5 Hz and 10 Hz. Further, the apparent mass of the participants walking in place was estimated between the values reported in the literature when standing in neutral position and when standing in neutral position with knee bent. Future works will include an electromyographical analysis of lower-limb muscles with respect to the excitation frequenc