AEROBIC AND ANAEROBIC METABOLISM DURING LOCOMOTION WITH TWO DIFFERENT WHEELCHAIR TYPES

Wheelchair design is extremely important in order to improve efficiency of locomotion and reduce physical stress in subjects whose muscular and cardiopulmonary fitness are impaired. Purpose of this study was to evaluate the effect of different wheelchair design on the aerobic and anaerobic metabolism during locomotion at different speeds in paraplegic subjects. The experiments were carried out on a group of 5 male paraplegic subjects (25 ±3 years; body weight 65±7kg) during locomotion on a roller ergometer (Sopur, Ergotronic mod.) at 3-4 different speeds from 2 to 9 km/h. At each speed oxygen consumption and heart rate were determined after at least 6 min of exercise. Lactic acid (LA) venous blood concentration was evaluated before and at the 5th min of recovery and lactate production was calculated. The oxygen equivalent of LA was assumed to be 3.15ml O2 per kg body weight for an increase of blood LA of 1 mmol/L. For each subject the test was repeated using two different types of daily use active wheelchairs: type A., foldable, 13.95kg; type B, demountable, 13.35kg. The main difference in size was in the horizontal location of the wheel axle, in seat height and in handrim diameter. Results indicate that: a) oxygen consumption increased linearly with speed being 2050±350ml/min and 1780±270ml/min at 9km/h for wheelchair type A and B, respectively; b)lactic acid concentrations were significantly higher, at a given speed, while using wheelchair type A than B (at 9km/h; 7.4±1.5 mmol/l and 6.0±1.6 mmol/l, respectively),c) the total energy required , aerobic and anaerobic, increased linearly with speed and was 15-20% higher with wheelchair type A than B at all speeds; d) the energy cost of locomotion at a given speed was in the 15-25% range higher for wheelchair A than B; e) at corresponding oxygen uptake, heart rate and pulmonary ventilation were not different with the two wheelchair types. The main results of this study concern the large difference existing in the energy cost of locomotion and in the lactate production in the same subject when two different wheelchairs, even if apparently similar are used. In particular the much higher lactate production suggests that wheelchair design affects the limb and trunk movements in such a way that the metabolism of some muscle group requires a greater participation of anaerobic mechanism of energy supply, this leading to early onset of muscular fatigue. Further studies, in particular the combined biomechanical analysis of user and wheelchair during locomotion are required to increase the optimum fitting of wheelchair –user interface

A simple method for measuring oxygen uptake on a single breath basis

A simple method for calculating breath by breath O2 uptake by the conventional open circuit method is described. Each expiratory volume is collected in a collapsible bag (4 l capacity) surrounded by a rigid box connected to a spirometer. A system of tubes with two solenoid valves operated by a manual switch allows the collection of air into the bag, during expiration, and its emptying by a vacuum pump during inspiration, respectively. The sampling line of a fast responding O2 and CO2 analyzer, together with temperature and pressure probes are inserted into the tube connecting the bag to the vacuum. The expired volume is therefore recorded (by the spirometer output) during expiration and its composition analyzed during the immediately following inspiratory phase, thus allowing gas exchange measurements to be performed on each single breath. VO2 measured by this method at steady state over periods of about 1 min yields substantially the same values as obtained by standard open circuit method (average ratio = 1.01). Ventilations up to 150 l/min (ATPS) and respiratory rates up to 60/min can be easily followed. The simplicity of VO2 calculation, and the very limited dead space of the system (about 70 ml, downstream the expiratory valve), make this method particularly suitable for determining VO2 kinetics at the onset and offset of exercise

EFFECT OF TRAINING AND SUDDEN DETRAINING ON THE PATELLAR TENDON AND ITS ENTHESIS IN RATS

Background: Different conditions may alter tendon characteristics. Clinical evidence suggests that tendon injuries are more frequent in athletes that change type, intensity and duration of training. Aim of the study was the assessment of training and especially detraining on the patellar tendon (PT) and its enthesis. Methods: 27 male adult Sprague-Dawley rats were divided into 3 groups: 20 rats were trained on a treadmill for 10 weeks. Of these, 10 rats were euthanized immediately after training (trained group), and 10 were caged without exercise for 4 weeks before being euthanized (de-trained group). The remaining 7 rats were used as controls (untrained rats). PT insertion, structure (collagen fiber organization and proteoglycan, PG, content), PT thickness, enthesis area, and subchondral bone volume at the enthesis were measured by histomorphometry and microtomography. Results: Both PG content and collagen fiber organization were significantly lower in untrained and detrained animals than in trained ones (p <0.05 and p < 0.0001). In the detrained group, fiber organization and PG content were worse than that of the untrained groups and the untrained group showed a significantly higher score than the detrained group (p < 0.05). In the trained group, the PT was significantly thicker than in untrained group (p < 0.05). No significant differences in the enthesis area and subchondral bone volume among the three groups were seen. Conclusions: Moderate exercise exerts a protective effect on the PT structure while sudden discontinuation of physical activity has a negative effect on tendons. The present results suggest that after a period of sudden de-training (such as after an injury) physical activity should be restarted with caution and with appropriate rehabilitation programs

Aerobic Training Affects Fatty Acid Composition of Erythrocyte Membranes

The effect of exercise training on the fatty acid composition of erythrocyte membranes was evaluated in an experimental animal model where rats were subjected to a ten-wk aerobic training. Five groups of rats were compared: sedentary rats at 19 or 23 wks of age, rats trained at moderate or high intensity sacrificed at 19 wks of age, and rats trained at high intensity, and sacrificed following 4 weeks of sedentary life. We had already demonstrated that cardioprotection correlates with training intensity and partially persists in detrained rats. Main findings are that rats trained at higher intensity display consistent signs of lipid peroxidation but a lower ω6/ω3 ratio and a lower content of trans fatty acids when compared to rats trained at lower intensity and to older sedentary rats. Trans fatty acids negatively affect cell membrane fluidity and permeability. Detrained rats showed intermediate values. Gene expression evaluation of selected enzymes involved in lipid biosynthesis revealed some of the adaptive mechanisms leading to the maintenance of membrane fatty acid homeostasis following exercise. The decrease in the amount of trans fatty and in the inflammatory pathways (i.e. ω6/ω3 ratio) in high-intensity trained rats underscores the protective effect of high intensity aerobic training

Oxygen affinity of blood in altitude Sherpas

Oxygen equilibrium curves on blood within 6 h from sampling have been estimated from polarographic measurements of oxyhemoglobin concentration, in 13 male 14- to 50-yr old Sherpas residing at 3,850 m above sea level (Kumjung, Nepal). In samples with red blood cell counts = 4.7 +/- 0.8 (SD) x 10(6)/mm3, total hemoglobin concentration [Hb] = 17.0 +/- 1.9 g/dl, and hematocrit = 53.3 +/- 5.0, the mean oxygen half-saturation of hemoglobin (P50) (pH = 7.4 and PCO2 = 40 Torr) was 27.3 +/- 1.8 Torr. The P50 of altitude Sherpas was not significantly different from that of acclimatized lowlanders (28.2 +/- 1.3; n = 7), sea-level Caucasian residents (26.5 +/- 1.0; n = 17), and Sherpas at sea level (27.1; n = 3). The 2,3-diphosphoglyceric acid-to-hemoglobin concentration ratio ([2,3-DPG]/[Hb]) in altitude Sherpas was 1.22 +/- 0.03, the same as that of acclimatized Caucasians (1.22 +/- 0.10). The Bohr effect measured for the blood of one altitude Sherpas by the ratio deltalog P50/deltapH was -0.32 and -0.45 at PCO2 levels of 40 and 20 Torr, respectively. These values are not significantly different from those found in Caucasians at sea level where deltalog P50/deltalpH was -0.35 and -0.42, respectively. It is concluded that the P50 in native highlanders is not significantly different from that observed in sea-level dwellers. [2,3-DPG]/[Hb] at altitude, both in natives and in newcomers, is 20% higher than in sea-level residents

Energy cost of walking with hip joint impairment

The energy cost of walking was measured in 12 patients (age 39-73 years) with hip joint impairment and 10 healthy controls during unassisted walking (2-6 km\ub7h -1) on a level treadmill surface and on a 5% incline. The energy cost of locomotion in most patients increased up to 50% and 70% during level-surface and uphill walking, respectively. This difference between patients and controls was probably due to the increased external mechanical work. The energy cost of walking, although related to pain experienced during walking but not hip joint range of motion or to joint status evaluated radiographically, provides an additional variable when defining the conditions of disability and functional impairment individuals with this pathological condition

Blood O2 affinity and maximal O2 consumption in elite bicycle racers

The PO2 at which hemoglobin is half-saturated with O2 (P50) at 37\ub0C, PCO2 = 42 Torr, measured pH and 2,3-diphosphoglycerate-to-hemoglobin concentration ratio ([2,3-DPG]/[Hb]) values, Hill's coefficient (n) at rest, and maximal O2 consumption (V\u307O2(max)) were determined in 11 world-class professional bicycle racers off-season (control, C), after 3 mo of 3 h daily training (preseason, PrS), and after additional 6 mo of competitions (competitive season, CoS). The results indicate that the P50 observed in trained athletes was the same as that of a comparable group of sedentary subjects (Sed) under the same conditions of pH, PCO2, and [2,3-DPG]/[Hb] and was similar to that obtained after 'normalization' in respect to pH and the [2,3-DPG]/[Hb]; [2,3-DPG]/[Hb] increased as a function of training from 0.72 to 0.95 (P < 0.001); the slope of the central portion of the O2 equilibrium curve (OEC) was nearly unaffected by endurance training as indicated by the n value (n(CoS) = 2.70 \ub1 0.08; n(Sed) = 2.65 \ub1 0.08); and V\u307O2(max) increased in the course of training 7 and 9% (P < 0.001), respectively, when expressed in absolute units or per kilogram body weight. The V\u307O2(max) predicted on the basis of a computer simulation does not increase significantly as a consequence of the measured rise in [2,3-DPG]. Therefore, the observed increase of V\u307O2(max) cannot be explained with adaptive changes of the OEC. The present results differ from previous findings reported in other types of athletes

The influence of mouth guard usage on neuromuscular activation and performance

Aim: The aim of this study was to investigate the effects of a commercially-available mouth guard (BRUX Mod. Sport) on neuromuscular activation and force capacity. Mouth guards, indeed, are commonly used in different sports to prevent injuries, but it is not yet clear whether they can influence the force expression and some athletes remain wary of the perceived potential performance detriments using them. Method: Ten participants completed a balanced randomized study with (S-MG) and without (Con) a sport mouth guard. Each participant performed two tests, with elbow flexors and knee extensors muscles: 1-min contraction at 100% of maximum voluntary contraction (MVC) and an 80% MVC contraction until exhaustion. During 80% MVC, the time of force within the target (t-target) and the coefficient of variation (CV) of the force signal were calculated. During 100% MVC, force decay (\uf044F%) and the root mean square (RMS) of the electromyogram (EMG) were calculated. Results: MVC values in S-MG were significantly higher than in Con in the elbow flexors (P<0.05). No differences was found in knee extensors muscles. At 80% MVC, no differences in t-target values were observed between Con and S-MG for both muscles group. Conversely, in knee extensors muscles, CV was significantly lower in S-MG compared to Con. During 1-min at 100% MVC contraction, \uf044F% was significantly lower in S-MG than in Con in the elbow-flexors (P<0.05) . Conclusion: Overall, these findings indicate that despite neuromuscular activation was not affected, S-MG usage increased maximum force production, endurance time and force stability, especially in the upper limb muscles. References - Dunn-Lewis, C, Luk, H-Y, Comstock, BA, Szivak, TK, Hooper, DR, Kupchak, BR, Watts, AM, Putney, BJ, Hydren, JR, Volek, JS, Denegar, CR, and Kraemer, WJ. The effects of a customized over-the-counter mouth guard on neuromuscular force and power production in trained men and women. J Strength Cond Res 26(4): 1085\u20131093, 2012. - Cetin, C, Kececi, AD, Erdogan, A, and Baydar, ML. Influence of custom-made mouth guards on strength, speed and anaerobic performance of taekwondo athletes. Dent Traumatol 25: 272\u2013276, 2009. - Bourdin M, Brunet-Patru I, Hager PE, Allard Y, Hager JP, Lacour JR et al. Influence of maxillary mouthguards on physiological parameters. Med Sci Sports Exerc 38:1500\u20134,2006

Comparison between continuous incremental ramp test and discontinuous square-wave test for vVO2max assessment in long distance runners and soccer players

Aim: In treadmill testing, the running velocity associated with maximum oxygen uptake (vVO2max) is largely utilized for both laboratory testing and training on the field. Differences between a continuous incremental ramp test (R1) and a discontinuous square wave tests (SW) in vVO2max assessment have been already described. Long distance runners and soccer players are both athletes involved with running. However, the physiological demands are different: in runners are continuous while in soccer players are discontinuous, with an alternation of aerobic and anaerobic tasks. Therefore, the aim of the study was to compare the vVO2max difference between R1 and SW in both these athletes. Hypothesis is that, this difference should be higher in soccer players than in runners, due to a different capacity to adjust the oxygen transport system at each workload. Method: Eight runners (RUN) and nine soccer players (SOC) reported to the laboratory twice to perform two maximum incremental tests: R1 (1 km/h per min) and SW (workloads of 4 min each, with 5 min of rest in between), in random order, on a motorised treadmill for VO2max and vVO2max assessment. At rest and during exercise, cardiorespiratory and metabolic parameters were collected breath-by-breath. Blood lactate concentration [La-] was measured at rest and at maximum exercise. Results: No significant differences between groups and protocols were found in VO2max (SOC: 3892\ub1104 vs 3922\ub1423 ml/min; RUN: 4159\ub1115 vs 4170\ub1116, for SW and R1, respectively), as well as in VE, VCO2, [La-]peak and HR at maximum exercise. However, vVO2max was significantly higher in R1 compared to SW in both groups (SOC: 16.1\ub10.3 vs 19.4\ub10.4 km/h, RUN: 19.5\ub10.3 vs 22.1\ub10.3 km/h, for SW and R1, respectively; P<0.05), with a higher difference between R1 vs SW in SOC than RUN (+21% vs +13%, respectively; P<0.05). Conclusion: Despite similar VO2max values, vVO2max was higher in R1 than in SW in both groups. However, the difference was significantly higher in SOC than RUN, possibly due to a slower capacity to adjust the oxygen transport system to a given workload in SOC. Even though the two protocols can be used to assess VO2max, the vVO2max differences between protocols must be acknowledged to prescribe correctly high intensity training, especially for soccer players

How physical exercise changes rat myotendinous junctions : an ultrastructural study

Myotendinous junctions can be easily injured by overloading or trauma, and exercise training may be a way of increasing their resistance to mechanical stress. To this end, we examined herein the morphological changes induced by moderate exercise training in the myotendinous junctions of extensor digitorum longus and gastrocnemius muscles in rats. Twelve Sprague-Dawley rats were used in this investigation. Six of them were trained to run on a treadmill for 1 h/day, 3 days/week over 10 weeks in order for them to achieve a running rate of 25 m/min at the end of the training period. Six age-matched sedentary rats were used as controls. The rats were sacrificed 24 h after the final training session, and the extensor digitorum longum (EDL) and the gastrocnemium were excised; the myotendinous junctions (MTJ) were then prepared and observed with electron microscopy. Digitation branching was evaluated by counting the bifurcations in the MTJ protrusions. Our observations indicate that exercise does indeed induce changes in MTJ morphology. In both muscles the number of bifurcated interdigitations increased significantly, as well as, in gastrocnemius, the branching of the finger-like processes. It was demonstrated that the MTJ is able to adapt to an increase in tensile force by enlarging the muscle-tendon contact area and, consequently, mechanical resistance