Reach to grasp kinematics and EMG analysis of C6 quadriplegic subjects

The aim of the present study was to assess the kinematics and the muscular activity of the upper limb of subjects suffering from a spinal cord injury (SCI) at the C6 level during a grasping task. Data were compared to a control group composed of able-bodied subjects. The electrical activity of six major upper limb muscles and 3D motion of the arm were recorded. Results showed higher relative muscular solicitation for C6 patients especially for deltoïdus posterior and the pectoralis major and modifications of the range of motion of the corresponding joint angles. It appeared that, for C6 SCI subjects, the role of shoulder complex is highly relevant to initiate and control upper extremity movement, and so is important for their autonomy. Such data may be used to help clinician in decision making, e.g. for reconstructive surgery by musculotendinous transfer.

Is impairment similar between arm and leg cranking exercise in COPD patients?

Impaired skeletal muscle function has been reported in patients with chronic obstructive disease (COPD), but such impairment is not homogenous and its distribution between the upper and the lower limbs is still unclear. The present study was designed to assess and compare upper and lower limb capacities in patients with moderate to severe COPD during incremental and constant-load exercises. Thirteen COPD patients of similar age with moderate to severe air flow limitation (FEV(1): 35%+/-5% predicted) and 19 healthy subjects were studied. Four sessions were organized: two incremental and two constant-load cycling exercises with arm or leg in randomized order. As observed in a previous study involving incremental and constant tests, power, VO(2), RER, VE, and HR were all significantly lower in the upper and lower limbs of patients with COPD than in healthy controls. In the healthy population, aerobic capacity and mechanical efficiency (ME) were lower in the course of arm exercises than in leg exercises. For the same relative workload, dyspnea and blood lactate production were higher during arm exercise. In contrast, no significant difference was observed between arm and leg capacities for any of these parameters in COPD patients.

CONCLUSION

Although aerobic capacity is impaired in COPD patients, arm aerobic capacity is relatively preserved. Given the lack of significant difference between arm and leg capacities in COPD, we hypothesize that upper limb muscles are less compromised than lower limb muscles in this patient population.

Effect of long duration exercise on the ratings of perceived exertion and perceived difficulty of walking and running at the ventilatory threshold

AIM

The purpose of this study was to examine if the relationship between physiological changes classically observed with exercise duration and some subjective workload measures would be affected by the complexity of the locomotion mode (running vs racewalking).

METHODS

The study was conducted on 24 well trained subjects (12 long distance runners and 12 racewalkers) divided in 3 groups (runners, racewalkers and control). Energy cost of locomotion (C), heart rate (HR), minute ventilation (V(E)), lactate concentration [La], ratings of perceived exertion (RPE 6-20 scale) and ratings of perceived difficulty (RPD 1(-1)5 scale) were recorded during 2 10-min submaximal tests on a treadmill before and immediately after a 3 hour exercise (racewalking or running) conducted at the velocity ventilatory threshold (vVT).

RESULTS

No significant variations in physiological parameters and perceived measures were observed in G(c). A significant increase (p<0.05) in energy cost of walking (mean: +9.4%) and running (mean: +7.5%) at the end of exercise was observed. A significant interaction of locomotion mode and exercise duration was found on perceived exertion and perceived difficulty. In racewalkers RPD significantly increased with duration whereas no significant effect was found for RPE. Conversely a significant increase in RPE was found after 3 hours in runners without any significant change in RPD.

CONCLUSIONS

This experiment suggests that, for a complex task, the classical relationship between RPE and metabolic load increase during prolonged exercise could be affected by changes in RPD. In this study, stability in RPE and increase in RPD observed in racewalkers may reflect an attentional focus dissociated from internal sensations and directed toward maintaining the required race walking gait.

Effect of two drafting modalities in cycling on running performance

PURPOSE

The purposes of this study were first to compare the physiological responses during a triathlon where cycling was performed alternatively with another cyclist (alternate draft triathlon, ADT) or continuously behind him (continuous draft triathlon, CDT), and second to study the incidence of these two drafting modalities in cycling on the subsequent running performance done during a simulated triathlon.

METHODS

Ten male triathletes of national level performed a sprint distance triathlon (0.75-km swim, 20-km bike, 5-km run) on two different sessions, one where the triathlete alternatively rode in front or at the back of another cyclist and rotating every 500 m, the other where the triathlete drafted continuously a professional cyclist whose task was to reproduce all split times recorded during the alternate situation. Oxygen uptake (VO2), expiratory flow (VE), heart rate (HR) were recorded during the entire bike and run sections and blood lactate concentrations ([La-]b) were analyzed at the end of each event composing the triathlon.

RESULTS

The results showed that expiratory flow, oxygen uptake, heart rate and blood lactate concentrations were significantly lower in CDT on the bike compared with drafting in alternation (148.1 vs. 167.2 L.min-1, 49.9 vs. 59.8 mL.min-1.kg-1, 154.7 vs. 173.1 beats.min-1, 3.5 vs. 6.3 mmol.L-1, respectively). The results also revealed that running after biking in CDT (for similar cycling speeds) significantly improved the subsequent running speed compared to ADT (17.87 vs. 17.15 km.h-1). Furthermore, VE, VO2, HR, and [La-]b were significantly higher during CDT run compared with ADT run (175.6 vs. 170.4 L.min-1, 69.7 vs. 66.8 mL.min-1.kg-1, 182.6 vs. 177.3 beats.min-1, 9.6 vs. 7.5 mmol.L-1, respectively).

CONCLUSIONS

These results showed that drafting continuously behind a lead cyclist allows triathletes to save a significant amount of energy during the bike leg of a sprint triathlon and creates the conditions for an improved running performance compared with a situation where cycling is performed alternating the lead with another cyclist.

Evolution of electromyographic signal, running economy, and perceived exertion during different prolonged exercises

The purpose of this study was to compare the electromyographic (EMG) signal of the vastus lateralis muscle obtained during a run section of a triathlon and at the end of a prolonged run performed at the same running velocity. Seven subjects were studied on three occasions: a 2 h 15 min triathlon (30 min swimming, 60 min cycling, and 45 min treadmill running at 75% of the maximal aerobic speed), a 2 h 15 min run, where the last 45 min (Prolonged Run, PR) were run at the same speed as the Triathlon Run (TR) on a motorized treadmill, and a 45 min Isolated Run (IR) performed at the same TR and PR velocity. The three experimental trials were randomised. Oxygen uptake (VO2), heart rate (HR), and EMG data were recorded during the three run sections. The results confirm a greater VO2 and HR during PR compared with IR (P<0.01) and TR (P<0.05). Also the VO2 values obtained during TR were significantly greater compared to IR (P < 0.05). EMG signal, obtained from the vastus lateralis muscle during 4 sec of isometric contraction at 35 % of maximal voluntary contraction (MVC), showed that after PR the mean power frequency (MPF) shifted significantly to lower frequencies (P<0.01) compared with MPF recorded before the prolonged run. Moreover, the signal amplitude (RMS) was increased significantly after PR in comparison to pre-trial (P < 0.01). Similar results were obtained for the TR at P < 0.05. The integrated EMG flow, QIEMG (iEMG/burst duration), recorded during all run sections, was significantly increased near the end of PR (i.e. 2 h 10 min of running) compared with QiEMG recorded after 1 h 30 min of running. No significant increase in QiEMG was observed with TR and IR situations. The results suggest that a long exercise bout of running led to a greater increase in muscle fatigue compared with a triathlon or an isolated run performed at the same running speed. In addition it is suggested that the rating of perceived exertion recorded during isometric contractions is a good indice to approach the level of fatigue during prolonged exercises.

Carbohydrate ingestion does not influence the change in energy cost during a 2-h run in well-trained triathletes

The aim of this study was to examine whether the increase in the energy cost of running (C(r)), previously reported to occur at the end of a prolonged run, could be influenced by the ingestion of either an artificially sweetened placebo (Pl) or a 5.5% carbohydrate (CHO) solution. Ten well-trained triathletes completed three testing sessions within a 3-week period. The aim of the first session was to determine maximal oxygen uptake (VO(2)(max)) and the velocity associated with ventilatory threshold (nu(VT)). The second and the third sessions were composed of two submaximal treadmill runs (20 min long, 0% grade, performed at nu(VT)), before and after an 80-min overground run, also conducted at nu(VT). During these submaximal tests, the subjects ingested (in a random order) either a Pl or CHO solution prior to the first submaximal run and every 20 min after that. During the first session, ventilatory threshold (VT) occurred at [mean (SD)] 81.2 (2.5)% VO(2)(max) and 16.5 (0.6) km. h(-1). A significant effect of exercise duration was found on C(r) (DeltaC(r)) at the end of the run, whatever the solution ingested (DeltaC(r) = 5.7% and 7.01% for CHO and Pl, respectively). A reduction in the respiratory exchange ratio (from 0.98 to 0.90) was observed only at the end of the Pl trial. In this study, C(r) seems to be affected only to a minor extent by substrate turnover. Moreover, the increase in the demand for oxygen, estimated from the increase in ventilation, accounted for only a minor proportion of the increase in C(r) (11% and 17% for CHO and Pl, respectively). No correlation was found between the changes in C(r) and the changes in the other physiological parameters recorded. These results suggest, indirectly, that C(r) increases during a 2-h run at 80% VO(2)(max) in well-trained subjects can be explained mainly by alterations in neuromuscular performance, which lead to a decrease in muscle efficiency.

Energetically optimal cadence vs. freely-chosen cadence during cycling: effect of exercise duration

The purpose of this study was to examine the relationship between cadence and oxygen consumption with exercise duration. Ten triathletes who trained regularly were examined. The first test was always a maximal test to determine maximal oxygen uptake (VO2max). The other sessions were composed of six submaximal tests representing 80% of the maximal power reached with VO2max (Pmax). During these tests submaximal rides with a duration of 30 min were performed. Each test represented, in a randomised order, one of the following pedal rates: 50, 65, 80, 95, 110 rpm and a freely-chosen rate. VO2, respiratory parameters, and heart rate were monitored continuously. Two periods, between the 3rd and the 6th minute and between the 25th and the 28th minute, were analysed. Results showed that when VO2 and heart rate were plotted against cadence, each curve could be best described by a parabolic function, whatever the period. Furthermore, a significant effect of period was found on energetically optimal cadence (70 +/- 4.5 vs. 86 +/- 6.2 rpm, P < 0.05). Only during the second period was no significant difference found between freely-chosen cadence (83 +/- 6.9 rpm) and energetically optimal cadence (P > 0.05). In conclusion, our results suggest that during prolonged exercise triathletes choose a cadence that is close to the energetically optimal cadence. A change of muscle fibre recruitment pattern with exercise duration and cadence would explain the shift in energetically optimal rate towards a higher pedal rate observed at the end of exercise.

Peak power and pulmonary oxygen uptake during knee extension exercise--comparisons among different incremental protocols

Four incremental protocols of knee extension exercise of different stage durations were compared to study the effect of the protocol upon power output at the last stage (Ppeak). Previous studies of knee extension have found very different power outputs with similar ergometers and these large differences have been interpreted as being the result of the fatigue due to the durations of the protocols. The knee extension device used in previous studies was modified to avoid the action of the knee and hip flexors: the subjects pushing on a lever instead of pulling a rod. In the present study five subjects performed four incremental knee extension exercises which differed with regard to stage duration (60, 90, 180 or 360 s) on this ergometer. The Ppeak, peak oxygen uptake (VO2peak) and peak heart rate (HRpeak) were measured at the end of each of these four incremental protocols. In eight subjects, the reliability of the protocols with the two shortest increments (60 and 90-s stages) was verified by measuring Ppeak at 60 s and 90 s (Ppeak60, Ppeak90) twice. The knee ergometer proposed in the present paper was easy to use without any special training and should improve the measurement of Ppeak. The Ppeak60 [49.4 (SD 5.6) W] was higher than at 180 s [Ppeak180), 43.6 (SD 5.8) W, P < 0.05] and at 360 s [Ppeak360, 43.4 (SD 5.3) W, P < 0.05]. All the other differences in Ppeak, VO2 peak and HRpeak were not significant. All correlations between Ppeak60, Ppeak90, Ppeak180 and Ppeak360 were significant, except those between Ppeak360 and Ppeak90 or Ppeak180. The effect of the stage duration on power output and oxygen uptake at the end of the knee extension exercises was not great. Consequently, the large differences in power output and oxygen uptake observed in previous studies cannot be explained by the protocol only. The significant difference between Ppeak 60 and Ppeak90 was of the order of 10% in agreement with findings in the literature using cycle ergometry. The reliability of Ppeak60 and Ppeak90 was high and the use of these protocols can be recommended if further studies show that the measurement of Ppeak, is useful in the evaluation of local endurance.

[Effect of a three month training period on the maximal oxygen deficiency in high level performance sprinters]

Recent studies have proposed the use of the maximal accumulated oxygen deficit (MAOD) as a useful alternative method to quantify individual anaerobic capacity (Green and Dawson, 1993; Medbø et al., 1988). Therefore, the aim of this research was to study the effect of a usual training procedure on maximal oxygen deficit and some other usual indicators of anaerobic capacity in elite 400-m runners (Lmax and Tlim). Eleven elite 400-m runners participated in this study. Each of them underwent two tests during two sessions before and after a training period. During these tests, MAOD, postexercise peak blood lactate (Lmax), oxygen uptake peak (VO2peak) and time to exhaustion (Tlim) were calculated or recorded. After the training period, the MAOD values decreased significantly contrary to VO2peak which increased by 8.84%. Furthermore a significant correlation was found between MAOD and VO2peak. From a training standpoint, MAOD appears to be sensitive to intense aerobic training in elite sprint runners, but it is very difficult to establish the utility of MAOD within an homogeneous high performance athletic population for 400 m training or performance optimisation.

Increase in energy cost of running at the end of a triathlon

The purpose of the present study was to verify the increase in energy cost of running at the end of a triathlon. A group 11 trained male subjects performed a triathlon (15-km swimming, 40-km cycling, 10-km running). At least 1 week later the subjects ran 10-km as a control at the same pace as the triathlon. Oxygen uptake (VO2), ventilation (VE) and heart rate (HR) were measured during both 10-km runs with a portable telemetry system. Blood samples were taken prior to the start of the triathlon and control run, after swimming, cycling, triathlon run and control run. Compared to the control values the results demonstrated that triathlon running elicited a significantly higher (P < 0.005) mean VO2 [51.2 (SEM 0.4) vs 47.8 (SEM 0.4) ml.min-1.kg-1] VE [86 (SEM 4.2) vs 74 (SEM 5.3) l.min-1], and HR [162 (SEM 2) vs 156 (SEM 1.9) beats.min-1)]. The triathlon run induced a greater loss in body mass than the control run [2 (SEM 0.2) vs 0.6 (SEM 0.2) kg], and a greater decrease in plasma volume [14.4% (SEM 1.5) vs 6.7% (SEM 0.9)]. The lactate concentrations observed at the end of both 10-km runs did not differ [2.9 (SEM 0.2) vs 2.5 (SEM 0.2) m.mol.l-1]. Plasma free fatty acids concentrations were higher (P < 0.01) after the triathlon than after the control run [1.53 (SEM 0.2) to 0.51 (SEM 0.07) mmol.l-1]. Plasma creatine kinase concentrations rose under both conditions from 58 (SEM 12) to 112 (SEM 14) UI.l-1 after the triathlon, and from 61 (SEM 7) to 80 (SEM 6) UI.l-1 after the control run. This outdoor study of running economy at the end of an Olympic distance triathlon demonstrated a decrease in running efficiency.

Effects of physical training in a hypobaric chamber on the physical performance of competitive triathletes

The effects of training in a hypobaric chamber on aerobic metabolism were studied in five high performance triathletes. During 3 weeks, the subjects modified their usual training schedule (approximately 30 h a week), replacing three sessions of bicycling exercise by three sessions on a cycle ergometer in a hypobaric chamber simulating an altitude of 4,000 m (462 mm Hg). Prior to and after training in the hypobaric chamber the triathletes performed maximal and submaximal exercise in normoxia and hypoxia (462 mm g). Respiratory and cardiac parameters were recorded during exercise. Lactacidaemia was measured during maximal exercise. Blood samples were drawn once a week to monitor blood cell parameters and erythropoetin concentrations. Training in the hypobaric chamber had no effect on erythropoiesis, the concentrations of erythropoetin always remaining unchanged, and no effect on the maximal oxygen uptake (VO2max) and maximal aerobic capacity measured in normoxia or hypoxia. Submaximal performance increased by 34% during a submaximal exhausting exercise performed at a simulated altitude of 2,000 m. During a submaximal nonexhausting test, ventilation values tended to decrease for similar exercise intensities after training in hypoxia. The changes in these parameters and the improved performance found for submaximal exercise may have been the result of changes taking place in muscle tissue or the result of training the respiratory muscles.