Effect of acute hypoxia on respiratory muscle fatigue in healthy humans

<p>Abstract</p> <p>Background</p> <p>Greater diaphragm fatigue has been reported after hypoxic versus normoxic exercise, but whether this is due to increased ventilation and therefore work of breathing or reduced blood oxygenation per se remains unclear. Hence, we assessed the effect of different blood oxygenation level on isolated hyperpnoea-induced inspiratory and expiratory muscle fatigue.</p> <p>Methods</p> <p>Twelve healthy males performed three 15-min isocapnic hyperpnoea tests (85% of maximum voluntary ventilation with controlled breathing pattern) in normoxic, hypoxic (SpO₂= 80%) and hyperoxic (FiO₂= 0.60) conditions, in a random order. Before, immediately after and 30 min after hyperpnoea, transdiaphragmatic pressure (P_di,tw) was measured during cervical magnetic stimulation to assess diaphragm contractility, and gastric pressure (P_ga,tw) was measured during thoracic magnetic stimulation to assess abdominal muscle contractility. Two-way analysis of variance (time x condition) was used to compare hyperpnoea-induced respiratory muscle fatigue between conditions.</p> <p>Results</p> <p>Hypoxia enhanced hyperpnoea-induced P_di,twand P_ga,twreductions both immediately after hyperpnoea (P_di,tw: normoxia -22 ± 7% vs hypoxia -34 ± 8% vs hyperoxia -21 ± 8%; P_ga,tw: normoxia -17 ± 7% vs hypoxia -26 ± 10% vs hyperoxia -16 ± 11%; all <it>P </it>< 0.05) and after 30 min of recovery (P_di,tw: normoxia -10 ± 7% vs hypoxia -16 ± 8% vs hyperoxia -8 ± 7%; P_ga,tw: normoxia -13 ± 6% vs hypoxia -21 ± 9% vs hyperoxia -12 ± 12%; all <it>P </it>< 0.05). No significant difference in P_di,twor P_ga,twreductions was observed between normoxic and hyperoxic conditions. Also, heart rate and blood lactate concentration during hyperpnoea were higher in hypoxia compared to normoxia and hyperoxia.</p> <p>Conclusions</p> <p>These results demonstrate that hypoxia exacerbates both diaphragm and abdominal muscle fatigability. These results emphasize the potential role of respiratory muscle fatigue in exercise performance limitation under conditions coupling increased work of breathing and reduced O₂transport as during exercise in altitude or in hypoxemic patients.</p

Estimativa das contribuições dos sistemas anaeróbio lático e alático durante exercícios de cargas constantes em intensidades abaixo do VO2max

O objetivo do estudo foi estimar as contribuições do metabolismo anaeróbio lático (MAL) e alático (MAA) em intensidades abaixo do consumo máximo de oxigênio (VO2max). Dez homens (23 ± 4 anos, 176,4 ± 6,8 cm, 72,4 ± 8,2 kg, 12,0 ± 4,5 % de gordura corporal) realizaram um teste progressivo até a exaustão voluntária para identificação do VO2max, da potência correspondente ao VO2max (WVO2max) e do segundo limiar ventilatório (LV2). Na segunda e na terceira visita foram realizados seis testes de cargas constantes (três testes por sessão) com intensidades abaixo do VO2max. Houve uma predominância do MAL sobre o MAA durante os exercícios submáximos a partir da intensidade correspondente ao LV2, sendo significativamente maior em 90% VO2max (p < 0,05). Dessa forma, esses resultados podem auxiliar treinadores a aplicarem cargas de treinamento adequadas aos seus atletas, de acordo com a exigência metabólica da competição

Mechanisms of attenuation of pulmonary V'O_{2} slow component in humans after prolonged endurance training

In this study we have examined the effect of prolonged endurance training program on the pulmonary oxygen uptake (V'O2 ) kinetics during heavy-intensity cycling-exercise and its impact on maximal cycling and running performance. Twelve healthy, physically active men (mean\ub1SD: age 22.33\ub11.44 years, V'O2peak 3198\ub1458 mL \ub7 min-1 ) performed an endurance training composed mainly of moderate-intensity cycling, lasting 20 weeks. Training resulted in a decrease (by 3c5%, P = 0.027) in V'O2 during prior low-intensity exercise (20 W) and in shortening of \u3c4 p of the V'O2 on-kinetics (30.1\ub15.9 s vs. 25.4\ub11.5 s, P = 0.007) during subsequent heavy-intensity cycling. This was accompanied by a decrease of the slow component of V'O2 on-kinetics by 49% (P = 0.001) and a decrease in the end-exercise V'O2 by 3c5% (P = 0.005). An increase (P = 0.02) in the vascular endothelial growth factor receptor 2 mRNA level and a tendency (P = 0.06) to higher capillary-to-fiber ratio in the vastus lateralis muscle were found after training (n = 11). No significant effect of training on the V'O2peak was found (P = 0.12). However, the power output reached at the lactate threshold increased by 19% (P = 0.01). The power output obtained at the V'O2peak increased by 14% (P = 0.003) and the time of 1,500-m performance decreased by 5% (P = 0.001). Computer modeling of the skeletal muscle bioenergetic system suggests that the training-induced decrease in the slow component of V'O2 on-kinetics found in the present study is mainly caused by two factors: an intensification of the each-step activation (ESA) of oxidative phosphorylation (OXPHOS) complexes after training and decrease in the "additional" ATP usage rising gradually during heavy-intensity exercise

Maximal leg-strength training improves cycling economy in previously untrained men

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A comparison of dietary intake between adult and veteran endurance athletes

This study compares the nutrient intake of young and veteran endurance athletes (veteran: >35 years). The purpose of the dietary analysis was to establish if any different nutritional practices were evident in older athletes. Three-day diet record data from 13 young (3 females; 24.0 ¡Ó 4.8 years; 71.7 ¡Ó 9.3 kg) and 16 veteran (3 Female; 43.8 ¡Ó 5.0 years; 71.7 ¡Ó 11.1 kg) endurance athletes were collected and compared for differences in nutrient intake and against accepted dietary guidelines. Diet records were analysed by a qualified dietitian using the dietary analysis software Food Works (Xyris Software, Highgate Hill, Australia). Physical activity levels were assessed using the Baecke physical activity questionnaire. Energy expenditure was also estimated using the equations of Schofield and Harris-Benedict. The results indicated that there were no significant differences between young and veteran athletes for overall energy intake. (12979 „b 3270 kJ vs 14234 „b 4485 kJ respectively). However, the veteran athletes had a significantly higher percentage of daily energy intake from fat than the young athletes (35„b5 vs. 29„b6 g.day-1; p<0.05). The mean dietary intake of carbohydrate for both age groups was substantially lower than the Australian Institute of Sport guidelines for endurance athletes. In conclusion, there were slight differences in fat intake between young and veteran endurance athletes plus both age groups may benefit by increasing daily carbohydrate intake

The effects of unilateral muscle fatigue on bilateral physiological tremor

The aim of this study was to examine the post-exercise effects of fatiguing the wrist extensor muscles of a single arm on postural tremor and muscle activity in both arms. Previous research has shown that, for neurologically normal subjects, the tremor seen within a single limb segment is uncorrelated to that seen contralaterally. However it has been speculated that some bilateral relation does exist, and that the nature of the relation may only become evident under conditions where the neuromuscular system is perturbed. To further investigate this potential bilateral relation, seven healthy subjects were required to adopt a bilateral postural pointing position after exercise-induced fatigue of the wrist extensor muscles of a single arm. Tremor from the forearm, hand and finger segments of each arm, surface EMG activity from extensor digitorum (ED) of each arm, and blood lactate data were collected prior to and after the exercise intervention. The main result was that fatiguing the distal muscles of one arm resulted in a bilateral increase in both the physiological tremor and ED activity. The change in tremor was confined to the index finger with no change in the tremor for the hand or forearm segments of either arm. While three peaks were seen in the frequency profile of the finger tremor, the effects of fatigue were confined to an increase in the peak power of the neurally generated 8-12 Hz tremor component. The contralateral increase in muscle activity was also reflected by a change in the frequency profile of the EMG output, with an increase in the peak power of both muscles following exercise of the wrist extensors of a single arm. The bilateral increases in physiological tremor and EMG activity of ED were only observed during the bilateral pointing task, with no changes in tremor or EMG activity seen for the non-exercised limb during the unilateral exercise protocol. The specificity of the resultant increases in the neurally generated 8-12 Hz component of finger tremor amplitude and EMG activity, coupled with the lack of any changes in tremor for the more proximal arm segments, indicate that these bilateral effects were mediated by an increase in the central neural drive to both limbs. Together this set of results challenges the general assumption of bilateral independence of tremor production, and further illustrate the task dependent nature of exercise-induced fatigue.Griffith Health, School of Rehabilitation SciencesNo Full Tex

Performance during consecutive days of laboratory time-trials in young and veteran cyclists

Aim. There is a common belief amongst athletes and coaches that older athletes need longer recovery time between training sessions and following competition. This study was undertaken to investigate the influence of age on recovery from high intensity endurance exercise in well-trained cyclists. Methods. Nine young and 9 veteran cyclists (mean±SD: young 24±5 years, veteran 45±6 years) performed 3 consecutive days (T1-T3) of laboratory based cycling time trials of 30-min duration (TT30). Mean power output, heart rate (HR), and blood lactate were measured throughout each TT30. Non-specific performance tests of fatigue were undertaken before and after the TT30 on each test day. Non-specific tests included, a maximal voluntary isometric contraction of the quadriceps muscle (MVIF), a countermovement jump (CMJ), a 10-s cycle sprint (10ST), and serum creatine kinase activity (CK). Results. Statistical analysis revealed that there were no significant group differences between young and veteran subjects for initial fitness or training status. Over T1-T3 both groups maintained average power during the TT30 (young and veteran results combined; 3.49±0.38,3.5±0.36 and 3.52±0.35 W·kg -1, T1-T3, respectively). For both groups serum CK activity was significantly elevated at T2 and T3, and mean HR during the TT30 was significantly lower at T3 (∼3 b·min -1). There were no group differences or significant within group interactions across the 3 days for MVIF or 10ST but there was a significantly lower CMJ height by T3 in both young and veteran (∼3%). MVIF was significantly lower after TT30 each day but had fully recovered by the following day. Conclusions. These findings suggest that high-intensity endurance performance is maintained in both well-trained young and veteran cyclists following 3 consecutive days of maximal 30-min laboratory time trials