Effects of two field continuous incremental tests on cardiorespiratory responses in Standardbred trotters.

In humans, cardiorespiratory responses are widely evaluated from field incremental exercise tests. On the contrary, equine exercise physiology faces a huge lack of oxygen consumption measurements (VO2) in field conditions due to technical concerns. The aim of this study was to test the effects of two incremental continuous field tests on cardiorespiratory responses in Standardbred trotters. The two protocols were realized at trot and ended when horses galloped. The tests started at 4.2 m/s (T1) and 6.4 m/s (T2), with speed increments of 1.4 m/s every 3 min for T1 and 0.8 m/s every 2 min for T2. Velocity (v), heart rate (HR) and gas exchanges were recorded continuously, and blood lactate concentration [La(-)] was measured before and after tests. Values recorded at the end of the tests were considered as peak values. The vpeak values were 10.6 ± 0.3 and 10.7 ± 0.7 m/s for T1 and T2 respectively. Horses reached higher VO2peak (T1: 116.6 ± 11.5 ml/min/kg; T2: 88.9 ± 10.2 ml/min/kg; p < 0.05) and HRpeak (T1: 217 ± 5 bpm; T2: 209 ± 3 bpm; p < 0.05) during T1 compared with T2. T1 was significantly longer than T2 (17.5 ± 1.9 vs. 12.9 ± 1.6 min respectively, p < 0.01), and the number of steps entirely ran tended to be different (T1: 5.6 ± 0.6; T2: 6.2 ± 0.8, p = 0.07). Compared to T2, the design of T1 appeared easier to implement and allowed higher cardiorespiratory responses. The relationship between HR-VO2 obtained through T1 gave a better correlation between the two variables than T2. These findings suggest that T1 might be better than T2 for evaluating cardiorespiratory adaptations to exercise and for estimating aerobic energy expenditure in exercising trotters.

Reproducibility, validity and responsiveness of the 200-metre fast walk test in patients undergoing cardiac rehabilitation.

OBJECTIVE: To investigate the reliability, validity and responsiveness of the 200-metre fast walk test in patients with coronary artery disease engaged in a cardiac rehabilitation programme. DESIGN: Descriptive study. SETTING: Tertiary care hospital. SUBJECTS: Thirty stable patients with coronary artery disease (51.9 ± 8.7 years), referred to the cardiac rehabilitation department after an acute coronary syndrome. INTERVENTION: Not applicable. MAIN MEASURES: Six-minute walk test distance, time to perform the 200-m fast walk test, peak power output of the graded maximal exercise test, before and after the programme; SF-36 quality of life questionnaire at baseline. Walk tests were performed twice at baseline to assess reliability. RESULTS: The 200-m fast walk test was highly reliable (ICC = 0.97). It was significantly correlated with the graded maximal exercise test peak power and the 6-minute walk test at baseline (r = -0.417; P < 0.05; and r = -0.566; P < 0.01, respectively) and after the training programme (r = -0.460, P < 0.05; and r = -0.926; P < 0.01, respectively). At baseline, there was a strong correlation between the 200-m fast walk test time and the physical component score of the SF-36 (r = -0.77; P < 0.01), but not between the 200-m fast walk test time and the SF-36 mental component score. Mean 200-m fast walk test time was significantly different between the patients performing ≤90 W (n = 11) or ≥100 W (n = 19) at the baseline graded maximal exercise test (121.7 ± 13.6 vs. 115.5 ± 10.1 seconds; P < 0.05). The responsiveness was strong with a standardized response mean at 1.11. CONCLUSION: The 200-m fast walk test is a reliable, valid and responsive high-intensity walk test in patients with coronary artery disease after an acute coronary syndrome. It can thus give additional information to that given by the 6-minute walk test and the graded maximal exercise test.

Does eccentric endurance training improve walking capacity in patients with coronary artery disease? A randomized controlled pilot study.

OBJECTIVE: To examine the effect of eccentric endurance training on exercise capacities in patients with coronary artery disease. DESIGN: Randomized parallel group controlled study. SETTING: Cardiac rehabilitation unit, Dijon University Hospital. PARTICIPANTS: Fourteen patients with stable coronary artery disease after percutaneous coronary intervention. INTERVENTION: Patients followed 15 sessions of training (1 session per day, 3 days a week), either in the concentric group, following a standard programme, or in the eccentric group, performing eccentric resistance exercises using both lower limbs on a specifically designed ergometer. MAIN OUTCOMES MEASURED: Symptom-limited Vo2, peak workload, isometric strength of leg extensor and ankle plantar flexors, distance covered during the 6-minute walk test and time to perform the 200-m fast walk test in both groups, before and after the training period. RESULTS: Patients did not report any adverse effects and were highly compliant. All measured parameters improved in eccentric and concentric group, except for 200-m fast walk test: symptom-limited Vo2 (+14.2% versus +4.6%), peak workload (+30.8% versus +19.3%), 6-minute walk test distance walked (+12.6% versus +10.1%) and leg extensor strength (+7% versus +13%) improved to a similar degree in both groups (P < 0.01); ankle plantar flexor strength improved in both groups with a significantly greater increase in the eccentric group (+17% versus +7%, P < 0.05). CONCLUSION: Patients with stable coronary artery disease can safely engage in eccentric endurance training, which appears to be as efficient as usual concentric training, with reduced oxygen consumption.

Low-frequency electromyostimulation and chronic heart failure.

Low-frequency electromyostimulation (EMS) acts on the skeletal muscle abnormalities that aggravate intolerance to effort in patients with chronic heart failure (CHF). It improves the oxidative capacity of muscles and thus enhances aerobic performance and physical capacity to almost the same degree, as does conventional physical training. No local or hemodynamic intolerance has been reported, even in cases of severe CHF. However, the presence of a pacemaker is one of the relative contra-indications (prior evaluation of tolerance is required), while that of an implanted defibrillator is one of the absolute contra-indications. EMS is an alternative to physical effort training when the latter is impossible due to a high degree of deconditioning or because there is a contra-indication, which may be temporary, due to the risk of acute decompensation and/or rhythm troubles. EMS can also be used in patients waiting for a heart transplant or in CHF patients who are unwilling to engage in physical activities. As EMS is not expensive and easy to set up, its use is likely to develop in the future.

Fatigue in patients with cardiovascular disease.

Fatigue is a frequent complaint during cardiovascular disease and can sometimes constitute the first clinical manifestation of this disease. It is responsible for deterioration of the quality of life and prognosis. Although physical and mental fatigue are often intimately interrelated, these two aspects of fatigue correspond to different pathophysiological mechanisms and different clinical features and the neurobiological links between the two are only just beginning to be studied. Physical fatigue is related to loss of efficacy of the effector muscle, due to multiple causes: mismatch of cardiac output during exercise, muscle and microcirculatory deconditioning, neuroendocrine dysfunction, associated metabolic disorders. Mental fatigue corresponds to predominantly depressive mood disorders with a particular entity, vital exhaustion. The diagnostic approach is designed to eliminate other organic causes of fatigue. Functional tests investigating physical (exercise capacity) and mental dimensions (mood disorders) can be used to analyse their respective roles and to propose personalized management, in which rehabilitation has an essential place due to its global approach. The objective of this reduction of fatigue is threefold: to improve independence, to improve quality of life and to limit morbidity and mortality.

[Assessment of physical activity in cardiovascular diseases]. / Indices de mesure de l'activité physique dans le domaine des affections cardiovasculaires.

PURPOSE: To identify the more useful among many methods available for the measurement of physical activity in patients with cardiovascular disease. For practical and financial reasons only questionnaires and mechanical monitoring, which are appropriate for use in large studies, were assessed. METHODS: To select tools valuable for clinical and epidemiological measurement of physical activity, with sufficient validity, reproducibility and sensitivity, we reviewed the literature in Medline with use of keywords: accelerometry, ambulatory accelerometry, ambulatory monitoring, cardiovascular diseases, daily activity, heart disease, pedometer, physical activity, questionnaire. RESULTS: Considering appropriate level of reproducibility and validity, 15 questionnaires are available. For measuring postures and motions during daily life, activity monitor seems to be more valid than pedometers or single accelerometers. CONCLUSION: At present the preferred method is a questionnaire, provided it is valid, repeatable, easy to use and inexpensive. In the future mechanical monitoring (especially activity monitor) will be probably a good alternative.

Technical note: Comparison of two methods to quantify exercise energy expenditure in trotters.

This study aimed at quantifying energy expenditure during 4 specific training exercises, that is, promenade, jogging, parcours, and interval exercises, using field measurements of oxygen consumption and heart rate in trotters. Six animals performed 2 preliminary tests to determine their individual maximum velocity and to establish their individual oxygen consumption/heart rate relationship from an incremental test. Then, they undertook each of the 4 specific exercises separated by 1 wk to avoid fatigue. The intensity of the 4 exercises was expressed in percent of individual maximum velocity as well as duration and distance set according to current training practices of French trotter trainers. Throughout the incremental test and the 4 exercises, oxygen consumption and heart rate were continuously recorded using a portable respiratory gas analyzer. Energy expenditure of the 3 different phases (warm-up, exercise, and recovery) of the 4 exercises and the total energy expended during exercises (sum of energy expended during the 3 phases) were calculated from direct oxygen uptake measurements and from estimated oxygen uptake using heart rate and O caloric equivalent. The quantification of total energy expenditure from the 2 methods was not significantly different. However, estimated energy expenditure was significantly lower from estimated oxygen consumption than direct oxygen uptake method concerning the warm-up and exercise phase of parcours. Our results indicate that the estimated oxygen uptake from heart rate measurements could be used to evaluate total energy expenditure of exercises in trotters. Whereas this method requires previous establishment of an individual oxygen consumption/heart rate curve, it is easy to record using commercially available instruments under practical conditions and opens new perspectives to assess energy balance in trotters' nutrition.

Quantification of the energy expenditure during training exercises in Standardbred trotters.

An appropriate energy feeding management that ensures the optimal dietary energy supply according to the energy expenditure (EE) is a crucial component for the horse's performance. The main purpose of this study was to determine the EE during four specific exercises used in the training of Standardbred trotters (promenade, jogging, parcours and interval work-outs). A total of six Standardbred geldings performed four different testing situations on a track. The intensity (expressed in percentage of the maximal velocity over 500 m, i.e. v500) and volume (distance and duration) of the testing situations were determined according to practices reported by French trainers. Promenade and jogging included only an exercise phase, whereas parcours and interval situations also included a warm-up and a recovery phase. Oxygen uptake (VO2), carbon dioxide production (VCO2) and heart rate (HR) were continuously recorded from 2 min before the beginning through to the end of the testing situations, using a portable respiratory gas analyser. Blood lactate levels and rectal temperature were determined before and immediately after the exercise phase of each testing situations. EE of the different phases (warm-up, exercise and recovery) and EE of the entire testing situations (EETOTAL) were calculated from VO2 measurements and the O2 caloric equivalent. Interval and parcours situations induced higher physiological responses than promenade and jogging situations, particularly in terms of VO2peak, VCO2peak and HRpeak. The highest blood lactate concentration (6 mmol/l) was measured after the interval exercise, and respiratory exchange ratios ⩾1 were observed only for the parcours situation. The EE of exercise phase varied from 0.49 to 1.79 kJ/min per kg for promenade and parcours situations. The EE of warm-up and recovery phases did not differ between parcours and interval situations, and was estimated at 1.04 and 0.57 kJ/min per kg BW, respectively. On average, the warm-up and the recovery phases contributed to 38% and 19% of the EETOTAL. For promenade, jogging, parcours and interval situations, EETOTAL was evaluated at 12 618, 11 119, 13 698 and 18 119 kJ, respectively.

Are first ventilatory threshold and 6-minute walk test heart rate interchangeable? A pilot study in healthy elderlies and cardiac patients.

BACKGROUND: Heart rate (HR) at the ventilatory threshold (VT) is often used to prescribe exercise intensity in cardiac rehabilitation. Some studies have reported no significant difference between HR at VT and HR measured at the end of a 6-min walk test (6-MWT) in cardiac patients. The aim of this work was to assess the potential equivalence between those parameters at the individual level. METHOD: Three groups of subjects performed a stress test and a 6-MWT: 22 healthy elderlies (GES, 77 ± 3.7 years), 10 stable coronary artery disease (CAD) patients (GMI, 50.9 ± 4.2 years) and 30 patients with chronic heart failure (GHF, 63.3 ± 10 years). We analyzed the correlation, mean bias, 95% confidence interval (95% CI) of the mean bias and the magnitude of the bias between 6-MWT-HR and VT-HR. RESULTS: There was a significant difference between 6-MWT and VT-HR in GHF (99.1 ± 8.8 vs 91.6 ± 18.6 bpm, P=0.016) but not in GES and GMI. The correlation between those 2 parameters was high for GMI (r=0.78, P<0.05), and moderate for GES and GHF (r=0.48 and 0.55, respectively, P<0.05). The 95% CI of bias was large (>30%) in GES and GHF and acceptable in GMI (8-12%). CONCLUSION: 6-MWT-HR and VT-HR do not appear interchangeable at the individual level in healthy elderlies and CHF patients. In CAD patients, further larger studies and/or the development of other walk tests could help in confirming the interest of a training prescription based on walking performance, after an exhaustive study of their cardiometabolic requirements.

Assessment of low-frequency fatigue with two methods of electrical stimulation.

The aim of this study was to compare the use of transcutaneous vs. motor nerve stimulation in the evaluation of low-frequency fatigue. Nine female and eleven male subjects, all physically active, performed a 30-min downhill run on a motorized treadmill. Knee extensor muscle contractile characteristics were measured before, immediately after (Post), and 30 min after the fatiguing exercise (Post30) by using single twitches and 0.5-s tetani at 20 Hz (P20) and 80 Hz (P80). The P20-to-P80 ratio was calculated. Electrical stimulations were randomly applied either maximally to the femoral nerve or via large surface electrodes (ES) at an intensity sufficient to evoke 50% of maximal voluntary contraction (MVC) during a 80-Hz tetanus. Voluntary activation level was also determined during isometric MVC by the twitch-interpolation technique. Knee extensor MVC and voluntary activation level decreased at all points in time postexercise (P < 0.001). P20 and P80 displayed significant time x gender x stimulation method interactions (P < 0.05 and P < 0.001, respectively). Both stimulation methods detected significant torque reductions at Post and Post30. Overall, ES tended to detect a greater impairment at Post in male and a lesser one in female subjects at both Post and Post30. Interestingly, the P20-P80 ratio relative decrease did not differ between the two methods of stimulation. The low-to-high frequency ratio only demonstrated a significant time effect (P < 0.001). It can be concluded that low-frequency fatigue due to eccentric exercise appears to be accurately assessable by ES.

The 200-m fast-walk test compared with the 6-min walk test and the maximal cardiopulmonary test: a pilot study.

OBJECTIVE: The 200-m fast-walk test has been proposed as a high- intensity performance test in healthy, elderly subjects. Adaptation of low-risk coronary artery disease patients during this test were compared with those in a 6-min walk test and a maximal cardiopulmonary exercise test. DESIGN: Thirty patients with stable coronary artery disease (51.9 +/- 8.7 yrs), referred to the cardiac rehabilitation department, performed a cardiopulmonary exercise test, then a 200-m fast-walk test and a 6-min walk test in a random order, before and after the training period (6 wks, 3 days per week). Heart rate was monitored during each test. Peak workload of cardiopulmonary exercise test, distance walked on the 6-min walk test, and time to perform the 200-m fast-walk test were measured. A subsample of ten patients performed the exercise test with gas exchange measurements, with ventilatory threshold determination. RESULTS: All subjects completed walk tests without complaint or incidents. Compared with the cardiopulmonary exercise test, the cardiac relative intensity was higher during the 200-m fast-walk test than during the 6-min walk test, both before (89.6% vs. 78.1% of cardiopulmonary exercise test maximal heart rate; P < 0.05) and after (83.8% vs. 74.3%; P < 0.05) training. Among the subsample of ten patients, the 200-m fast-walk test heart rate was significantly higher than the ventilatory threshold heart rate, which did not differ from the 6-min walk test heart rate. The 200-m fast-walk test time significantly decreased after training (-9.1%, P < 0.01). CONCLUSION: In patients with coronary artery disease at low risk, the 200-m fast-walk test explores higher levels of cardiorespiratory capacity than the 6-min walk test. Thus, this could be a useful field test in complement to the cardiopulmonary exercise test to assess functional capacity improvement and update training targets regularly during the course of high-intensity rehabilitation programs in this population.

Effects of two types of fatigue on the VO(2) slow component.

The aim of the study was to test the hypothesis of the involvement of type II fibres in the V.O (2) slow component phenomenon by using two prior fatiguing protocols on the knee extensor muscles. Nine subjects performed three constant-load cycling exercises at a work rate corresponding to 80 % of their V.O (2) max: (i) preceded by a 20-min fatiguing protocol using electromyostimulation (EMS), (ii) preceded by a 20-min fatiguing protocol using voluntary contractions (VOL), and (iii) without fatiguing protocol (NFP). Voluntary and evoked neuromuscular properties of the knee extensor muscles were tested before (PRE) and after (POST) the two fatiguing protocols. Results show a significant reduction in voluntary force after both fatiguing protocols (-19.9 % and -11.8 %, in EMS and VOL, respectively p<0.01). After EMS, this decrease was greater than after VOL (p<0.05) and was combined with a slackening of muscle contractile properties which was absent after VOL (p<0.05). Regarding the effects on oxygen uptake kinetics, the appearance of the slow component was delayed after EMS and its amplitude was lower than those obtained in VOL and NFP conditions (0.48+/-0.07 vs. 0.75+/-0.09 and 0.69+/-0.08 L . min (-1), respectively; p<0.05). It can thus be concluded that exercises dedicated to preferentially fatiguing type II fibres may alter V.O (2) kinetics.