Raffaele Milia

Physiological responses and energy cost during a simulation of a Muay Thai boxing match

Muay Thai is a martial art that requires complex skills and tactical excellence for success. However, the energy demand during a Muay Thai competition has never been studied. This study was devised to obtain an understanding of the physiological capacities underlying Muay Thai performance. To that end, the aerobic energy expenditure and the recruitment of anaerobic metabolism were assessed in 10 male athletes during a simulation match of Muay Thai. Subjects were studied while wearing a portable gas analyzer, which was able to provide data on oxygen uptake, carbon dioxide production, and heart rate (HR). The excess of CO2 production (CO2 excess) was also measured to obtain an index of anaerobic glycolysis. During the match, group energy expenditure was, on average (mean +/- standard error of the mean), 10.75 +/- 1.58 kcal.min-1, corresponding to 9.39 +/- 1.38 metabolic equivalents. Oxygen uptake and HRs were always above the level of the anaerobic threshold assessed in a preliminary incremental test. CO2 excess showed an abrupt increase in the first round, and reached a value of 636 +/- 66.5 mL.min-1. This parameter then gradually decreased throughout the simulation match. These data suggest that Muay Thai is a physically demanding activity with great involvement of both the aerobic metabolism and anaerobic glycolysis. In particular, it appears that, after an initial burst of anaerobic glycolysis, there was a progressive increase in the aerobic energy supply. Thus, training protocols should include exercises that train both aerobic and anaerobic energetic pathways.

Role of heart rate and stroke volume during muscle metaboreflex-induced cardiac output increase: differences between activation during and after exercise

We hypothesized that the role of stroke volume (SV) in the metaboreflex-induced cardiac output (CO) increase was blunted when the metaboreflex was stimulated by exercise muscle ischemia (EMI) compared with post-exercise muscle ischemia (PEMI), because during EMI heart rate (HR) increases and limits diastolic filling. Twelve healthy volunteers were recruited and their hemodynamic responses to the metaboreflex evoked by EMI, PEMI, and by a control dynamic exercise were assessed. The main finding was that the blood pressure increment was very similar in the EMI and PEMI settings. In both conditions the main mechanism used to raise blood pressure was a CO elevation. However, during the EMI test CO was increased as a result of HR elevation whereas during the PEMI test CO was increased as a result of an increase in SV. These results were explainable on the basis of the different HR behavior between the two settings, which in turn led to different diastolic time and myocardial performance.

Estimating stroke volume from oxygen pulse during exercise.

This investigation aimed at verifying whether it was possible to reliably assess stroke volume (SV) during exercise from oxygen pulse (OP) and from a model of arterio-venous oxygen difference (a-vO(2)D) estimation. The model was tested in 15 amateur male cyclists performing an exercise test on a cycle-ergometer consisting of a linear increase of workload up to exhaustion. Starting from the analysis of previous published data, we constructed a model of a-vO(2)D estimation (a-vO(2)D(est)) which predicted that the a-vO(2)D at rest was 30% of the total arterial O(2) content (CaO(2)) and that it increased linearly during exercise reaching a value of 80% of CaO(2) at the peak workload (W(max)) of cycle exercise. Then, the SV was calculated by applying the following equation, SV = OP/a-vO(2)D(est), where the OP was assessed as the oxygen uptake/heart rate. Data calculated by our model were compared with those obtained by impedance cardiography. The main result was that the limits of agreement between the SV assessed by impedance cardiography and the SV estimated were between 22.4 and -27.9 ml (+18.8 and -24% in terms of per cent difference between the two SV measures). It was concluded that our model for estimating SV during effort may be reasonably applicable, at least in a healthy population.

A paradigm of uphill running.

The biomechanical management of bioenergetics of runners when running uphill was investigated. Several metabolic and mechanical variables have been studied simultaneously to spread light on the locomotory strategy operated by humans for effective locomotion. The studied variables were: heart rate, heart rate variability, oxygen intake and blood lactate, metabolic cost, kinematics, ground reaction force and muscular activity. 18 high-level competitive male runners ran at 70% VO2max on different uphill slope conditions: 0%, 2% and 7%. Modifications were significant in almost all variables studied, and were more pronounced with increasing incline. Step frequency/length and ground reaction force are adjusted to cope with both the task of uphill progression and the available (limited) metabolic power. From 0% to 7% slope, step frequency and ground reaction force and metabolic cost increased concurrently by 4%, 12% and 53%, respectively (with a 4% step length decrease as well). It is hypothesised that this biomechanical management is allowed by an environment-body communication performed by means of specific muscular activity.

Haemodynamic effect of metaboreflex activation in men after running above and below the velocity of the anaerobic threshold

Previous studies have shown that the muscle metaboreflex, along with its effect on peripheral vasculature, is capable of inducing substantial enhancement in cardiac performance, stroke volume and cardiac output. This study was designed to determine whether the metaboreflex recruited by means of postexercise muscle ischaemia (PEMI) after running at two intensities was capable of eliciting similar enhancement in these cardiovascular parameters. In eight healthy male athletes the metaboreflex was studied with the PEMI method at the start of recovery from running bouts at a velocity of 30% above (PEMI‐AVAT) or below (PEMI‐BVAT) the anaerobic threshold previously assessed. Control exercise recovery tests at the same intensities were also conducted. Haemodynamics were evaluated by means of impedance cardiography. The main results were that: (1) the PEMI‐AVAT test induced an increase in stroke volume, which was not present during the other protocol conditions; (2) the PEMI‐AVAT test also induced a blunted heart rate response compared with the control situation, but this relative bradycardia was fully compensated by the stroke volume increment so that cardiac output was maintained and even increased in comparison with the other protocol sessions; and (3) finally, there was no detectable increase in systemic vascular resistance during PEMI‐AVAT. These results provide evidence that, like what has previously been reported for small muscle mass exercise, metaboreflex activation after running is capable of enhancing cardiac performance and stroke volume. Moreover, this study strengthens the concept that the cardiovascular response to metaboreflex is not merely the consequence of an increase in systemic vascular resistance.

Hemodynamic responses to metaboreflex activation: insights from spinal cord-injured humans

This investigation was conducted to study the hemodynamic consequences of spinal cord injury (SCI) during post-exercise muscle metaboreflex activation in SCI subjects. The hemodynamic response to metaboreflex recruitment was assessed in ten SCI patients and nine healthy controls (CTL) by means of impedance cardiography. The main results were (1) the metaboreflex-induced blood pressure rise was blunted in SCI subjects compared with normals, (2) the CTL group achieved the blood pressure response via cardiac output increase, while the SCI subjects could not use this mechanism, (3) the CTL group was able to enhance stroke volume and ventricular filling rate in response to the metaboreflex, whereas the SCI group could not. It was concluded that in healthy individuals, the hemodynamic response to the metaboreflex is an integrated phenomenon that depends mainly on a flow-mediated mechanism, whereas in SCI individuals the reduced venous return impairs this mechanism.

Effect of Beetroot Juice Supplementation on Aerobic Response during Swimming

The beneficial effects of beetroot juice supplementation (BJS) have been tested during cycling, walking, and running. The purpose of the present study was to investigate whether BJS can also improve performance in swimmers. Fourteen moderately trained male master swimmers were recruited and underwent two incremental swimming tests randomly assigned in a pool during which workload, oxygen uptake (VO2), carbon dioxide production (VCO2), pulmonary ventilation (VE), and aerobic energy cost (AEC) of swimming were measured. One was a control swimming test (CSW) and the other a swimming test after six days of BJS (0.5l/day organic beetroot juice containing about 5.5 mmol of NO3−). Results show that workload at anaerobic threshold was significantly increased by BJS as compared to the CSW test (6.3 ± 1 and 6.7 ± 1.1 kg during the CSW and the BJS test respectively). Moreover, AEC was significantly reduced during the BJS test (1.9 ± 0.5 during the SW test vs. 1.7 ± 0.3 kcal·kg−1·h−1 during the BJS test). The other variables lacked a statistically significant effect with BJS. The present investigation provides evidence that BJS positively affects performance of swimmers as it reduces the AEC and increases the workload at anaerobic threshold.

Altered hemodynamics during muscle metaboreflex in young type 1 diabetes patients

A reduction in catecholamine levels during exercise has been described in young subjects with type 1 diabetes mellitus (DM1). It has been suggested that type 1 diabetes per se is associated with the loss of sympathetic response before any clinical evidence. Considering that an increase in sympathetic drive is required for normal cardiovascular response to muscle metaboreflex, the aim of this study was to assess the hemodynamics during metaboreflex in DM1 patients. Impedance cardiography was used to measure hemodynamics during metaboreflex activation, obtained through postexercise ischemia in 14 DM1 patients and in 11 healthy controls (CTL). Principal results were: 1) blunted blood pressure response during metaboreflex was observed in DM1 patients compared with the CTL; 2) reduced capacity to increase systemic vascular resistance was also witnessed in DM1 subjects; 3) DM1 subjects reported higher stroke volumes as a consequence of reduced cardiac afterload compared with the CTL, which led to a more evident cardiac output response, which partially compensated for the lack of vasoconstriction. These facts suggest that cardiovascular regulation was altered in DM1 patients and that there was a reduced capacity to increase sympathetic tone, even in the absence of any overt clinical sign. The metaboreflex test appears to be a valid tool to detect early signs of this cardiovascular dysregulation.

Effects of acute vasodilation on the hemodynamic response to muscle metaboreflex

The aim of the present study was to test the contribution of stroke volume (SV) in hemodynamic response to muscle metaboreflex activation in healthy individuals. We hypothesized that an acute decrease in cardiac afterload and preload due to the administration of a vasodilating agent could reduce postexercise muscle ischemia (PEMI)-induced SV response. Ten healthy males (age 33.6 ± 1.3 yr) were enrolled and randomly assigned to the following study protocol: 1) PEMI session, 2) control exercise recovery (CER) session, 3) PEMI after sublingual administration of 5 mg of isosorbide dinitrate (ISDN), and 4) CER after ISDN. Central hemodynamics were evaluated by means of impedance cardiography. The main findings were a blunted SV response during metaboreflex following acute arterial and venous vasodilation, associated with a reduction in cardiac diastolic time and filling, and a decrement of systemic vascular resistance. These hemodynamic changes restrain blood pressure response during metaboreflex activation. Our results indicate that hemodynamic response to metaboreflex activation is a highly integrated phenomenon encompassing complex interplay between heart rate, cardiac performance, preload, and afterload and that impairment of one or more of these parameters leads to altered hemodynamic response to metaboreflex.

Progressive improvement in hemodynamic response to muscle metaboreflex in heart transplant recipients

Exercise capacity remains lower in heart transplant recipients (HTRs) following transplant compared with normal subjects, despite improved cardiac function. Moreover, metaboreceptor activity in the muscle has been reported to increase. The aim of the present investigation was to assess exercise capacity together with metaboreflex activity in HTR patients for 1 yr following heart transplant, to test the hypothesis that recovery in exercise capacity was paralleled by improvements in response to metaboreflex. A cardiopulmonary test for exercise capacity and Vo(2max) and hemodynamic response to metaboreflex activation obtained by postexercise ischemia were gathered in six HTRs and nine healthy controls (CTL) four times: at the beginning of the study (T0, 42 ± 6 days after transplant), at the 3rd, 6th, and 12th month after TO (T1, T2, and T3). The main results were: 1) exercise capacity and Vo(2max) were seen to progressively increase in HTRs; 2) at T0 and T1, HTRs achieved a higher blood pressure response in response to metaboreflex compared with CTL, and this difference disappeared at T2 and T3; and 3) this exaggerated blood pressure response was the result of a systemic vascular resistance increment. This study demonstrates that exercise capacity progressively improves in HTRs after transplant and that this phenomenon is accompanied by a progressive reduction of the metaboreflex-induced increase in blood pressure and systemic vascular resistance. These facts indicate that, despite improved cardiac function, resetting of cardiovascular regulation in HTRs requires months.