Differences in quadriceps muscle strength and fatigue between lean and obese subjects

The present study aimed to compare quadriceps femoris muscle strength and fatigue between obese (grade II and III) and nonobese adults. Ten obese (mean age: 25 years; mean BMI: 41 kg/m2) and ten lean (mean age: 27 years; mean BMI: 23 kg/m2) men were tested. Quadriceps muscle fatigue was quantified as the (percent) torque loss during a voluntary isokinetic (50 maximal contractions at 180°/s) and an electrostimulated (40 Hz) isometric protocol (5 min, 10% of the maximal torque). Maximal voluntary isometric and isokinetic torque and power were also measured. Voluntary torque loss was significantly higher (P < 0.05) in obese (−63.5%) than in lean subjects (−50.6%). Stimulated torque decreased significantly (P < 0.05) but equally in the two subject groups. Obese subjects displayed higher absolute (+20%; P < 0.01) but lower relative (i.e., normalized to body mass) (−32%; P < 0.001) muscle torque and power than their lean counterparts. Obese individuals demonstrated lower fatigue resistance during voluntary but not during stimulated knee extensions compared to their nonobese counterparts. Peripheral mechanisms of muscle fatigue—at least those associated to the present stimulated test—were not influenced by obesity. The observed quadriceps muscle function impairments (voluntary fatigue and relative strength) probably contribute to the reduced functional capacity of obese subjects during daily living activities.     

Linkage between oxygen uptake at ventilatory threshold and muscle strength in subjects with and without metabolic syndrome

We evaluated the linkage between oxygen uptake at the ventilatory threshold (VT) and muscle strength in subjects with and without metabolic syndrome. We used data of 226 Japanese men with metabolic syndrome and 265 Japanese men without the syndrome. Metabolic syndrome has recently been defined by a new criterion in Japan. Oxygen uptake at VT and muscle strength, i.e. grip strength and leg strength were measured. Oxygen uptake at VT and muscle strength/body weight were found to be significantly lower in subjects with metabolic syndrome than in those without the syndrome. However, the differences did not reach significant levels after adjusting for leg strength/body weight or oxygen uptake at VT. A combination of aerobic exercise and resistance training might be considered for preventing and improving metabolic syndrome.     

Effect of maximal oxygen uptake and different forms of physical training on serum lipoproteins

Summary 260 well trained male sportsmen between 17 and 30 years of age participating in a variety of events were examined for total serum cholesterol and lipoprotein cholesterol and compared with 37 moderately active leisure-time sportsmen and 20 sedentary controls of similar ages and sex. Lipoprotein cholesterol distribution was determined by quantitative electrophoresis.Mean HDL-cholesterol increased progressively from the mean of the sedentary controls to the mean of the long-distance runners, indicating a graded effect of physical activity on HDL-cholesterol. In all sporting groups mean LDL-cholesterol tended to be lower than in the controls, no association between LDL-cholesterol and form of training being apparent. Except for the long-distance runners, all sporting groups tended to be lower in total cholesterol than the controls. The HDL-/total cholesterol and LDL/HDL ratios yielded a better discrimination between the physically active and inactive than the HDL-cholesterol alone.Significant positive correlations with maximal oxygen uptake and roentgenologically determined heart volume were found for HDL-cholesterol and HDL-/total cholesterol, and negative ones for LDL/HDL. Differences in the regressions among subsets made up of sporting groups under different physical demands suggest a positive relationship between lipoprotein distribution and the magnitude of the trained muscle mass.With support of Bundesinstitut für Sportwissenschaft, Köln-Lövenich     

Relationship between record time and maximal oxygen consumption in middle-distance running

Summary The relationship between record time (t _r) and maximal oxygen uptake ( ) has been examined in 69 male physical education students who had taken part in 800-m and 1500-m footraces. It was found thatt _r and were inversely related. The relationshipst _r=f( ) have been fitted by two exponential equations:t _r(1500 m)=698e –0.0145 t _r(800 m) = 272e^–0.01 P<0.001. A mathematical formulation of the energy conservation principle in supramaximal running, based on the exponential increase of the oxygen uptake as a function of time with a rate constant of 0.025 s^–1 has been applied to thet _r calculation from . As calculatedt _r were highly correlated to measuredt _r (P<0.001), it was concluded that the relationshipst _r=f( ) can be interpreted on the basis of the model described in this study.     

Hyperthermia and maximal oxygen uptake in men and women

To compare the effect of hyperthermia on maximal oxygen uptake (O_2max) in men and women, O_2max was measured in 11 male and 11 female runners under seven conditions involving various ambient temperatures (T_a at 50% RH) and preheating designed to manipulate the esophageal (T_es) and mean skin temperatures at O_2max. The conditions were: 25°C, no preheating (control); 25, 35, 40, and 45°C, with exercise-induced preheating by a 20-min walk at ~33% of control O_2max; 45°C, no preheating; and 45°C, with passive preheating during which T_es and were increased to the same degree as at the end of the 20-min walk at 45°C. Compared to O_2max (l·min^–1) in the control condition (4.52±0.46 in men, 3.01±0.45 in women), O_2max in men and women was reduced with exercise-induced or passive preheating and increased T_a, ~4% at 35°C, ~9% at 40°C and ~18% at 45°C. Percentage reductions (7–36%) in physical performance (treadmill test time to exhaustion) were strongly related to reductions in O_2max (r=0.82–0.84). The effects of hyperthermia on O_2max and physical performance in men and women were almost identical. We conclude that men and women do not differ in their thermal responses to maximal exercise, or in the relationship of hyperthermia to reductions in O_2max and physical performance at high temperature. Data are reported as mean (SD) unless otherwise stated.     

The comparison of peak oxygen uptake between swim-bench exercise and arm stroke

To compare maximal cardio-respiratory stress between swim-bench exercise (SB) and arm stroke (AS), peak oxygen uptake (VO_{2 peak}) was measured in six trained swimmers. The SB was performed at stroke frequency of 50 · min^–1. Oxygen uptake (VO₂) was measured during exercise at 3-min constant exercise intensities in SB and at 4-min constant water flow rates in AS. We measured a steady-state VO₂ within 3 or 4 min after the beginning of each exercise. The exercise intensity or the water flow rate was increased by 14.7 W or by 0.05 m · s^–1, respectively, until a levelling-off of VO₂ was observed. The VO₂ was measured by the Douglas bag method. Heart rate (HR) and blood lactate concentration ([1a^–]_b) were determined at the exercise intensity and the water flow rate at which VO_{2 peak} was obtained. At submaximal levels, VO₂ increased in proportion to exercise intensity for SB and to the water flow rate for AS. A levelling-off of VO₂ was observed in all subjects for both kinds of exercise. The VO₂ during SB [2.13 (SD 0.25)1 · min^–1] was significantly lower than that during AS [2.72 (SD 0.39)1 · min^–1] and corresponded to 78.9 (SD 7.0)% of AS VO_{2 peak}. Maximal HR during SB was also significantly lower than that during AS. No significant differences between SB and AS were found for either pulmonary ventilation or [1a^–]_b. The peak exercise duration in SB [2.4 (SD 0.5) min] was significantly shorter than that in As [3.6 (SD 0.5) min]. These results would suggest that even though both kinds of exercise use the muscles of the upper body, active muscle groups involved during SB are different and/or smaller, and maximal stress on the cardio-respiratory system is lower when compared to AS.     

Relationship between oxygen uptake kinetics and performance in repeated running sprints

The purpose of this study was to test the hypothesis that subjects having a shorter time constant for the fast component of kinetics in a transition from rest to constant exercise would maintain their speed for a longer time during repeated sprint exercise (RSE). Eleven male soccer players completed a graded test, two constant exercises at 60% maximal aerobic speed and RSE, consisting of fifteen 40-m sprints alternated with 25 s of active recovery. All the tests were performed on the field (200 m indoor track). The parameters of the kinetics (time delay, time constant, and amplitude of the primary phase) during the two constant exercises were modeled. All subjects elicited during the RSE. A significant correlation was found between and the relative decrease in speed during the 15 sprints (r=0.71; p < 0.05), but not between and the cumulated time for the 15 sprints (r=0.48; p > 0.05). There were significant correlations between the time constant of the primary phase and the relative decrease in speed during the 15 sprints (r=0.80; p < 0.01) and the cumulated time for the 15 sprints (r=0.80; p < 0.01). These results suggest that individuals with faster kinetics during constant load exercise might also have a faster adjustment of during RSE leading to a shorter cumulated time and a lower relative decrease in speed during the 15 sprints.     

Ventilatory threshold and maximal oxygen uptake in present triathletes.

The aim of this study was to determine the physiological profile of young triathletes who began triathlon competition as their first sport. Twenty-nine male competitive triathletes (23 regionally and nationally ranked triathletes and 6 elite, internationally ranked triathletes) performed two tests, one on a cycle ergometer (CE VO2max) and one on a treadmill (TM VO2max). Results showed (a) no difference between CE VO2max and TM VO2max in the triathletes (69.1 +/- 7.2 vs. 70.2 +/- 6.2 mL x kg(-1) x min(-1), respectively), (b) values of CE VO2max and TM VO2max in elite triathletes (75.9 +/- 5.2 and 78.5 +/- 3.6 mL x kg(-1) x min(-1), respectively) that were comparable to those reported in elite single-sport athletes in these specialities, and (c) although the ventilatory threshold (Th(vent)) was similar in CE and TM, TM Th(vent) was consistently lower for triathletes than TM Th(vent) usually reported for runners.     

Relationship between muscle fatigue and oxygen uptake during cycle ergometer exercise with different ramp slope increments

Summary The surface electromyogram (EMG) from active muscle and oxygen uptake ( ) were studied simultaneously to examine changes of motor unit (MU) activity during exercise tests with different ramp increments. Six male subjects performed four exhausting cycle exercises with different ramp slopes of 10, 20, 30 and 40 W · min^–1 on different days. The EMG signals taken from the vastus lateralis muscle were stored on a digital data recorder and converted to obtain the integrated EMG (iEMG). The was measured, with 20-s intervals, by the mixing chamber method. A non-linear increase in iEMG against work load was observed for each exercise in all subjects. The break point of the linear relationship of iEMG was determined by the crossing point of the two regression lines (iEMG_bp). Significant differences were obtained in the exercise intensities corresponding to maximal oxygen uptake ( ) and the iEMG_bp between 10 and 30, and 10 and 40 W · min –1 ramp exercises (P < 0.05). However, no significant differences were obtained in and corresponding to the iEMG_bp during the four ramp exercises. With respect to the relationship between and exercise intensity during the ramp increments, the -exercise intensity slope showed significant differences only for the upper half (i.e. above iEMG_bp). These results demonstrated that the and at which a nonlinear increase in iEMG was observed were not varied by the change of ramp slopes but by the exercise intensity corresponding to and the iEMG_bp was varied by the change of ramp slopes. In addition, the significant differences in the exercise intensity slopes for the upper half of the tests would suggest that the recruitment patterns of MU and/or muscle metabolic state might be considerably altered depending upon the ramp slope increments.     

The influence of PaO2, pH and SaO2 on maximal oxygen uptake

Influence of arterial oxygen pressure (P_aO₂) and pH on haemoglobin saturation (S_aO₂) and in turn on O₂ uptake (VO ₂) was evaluated during ergometer rowing (156, 276 and 376 W; VO _2max, 5.0 L min^?1; n = 11). During low intensity exercise, neither pH nor S_aO₂ were affected significantly. In response to the higher work intensities, ventilations (V_E) of 129 ± 10 and 155 ± 8 L min^?1 enhanced the end tidal PO₂ (P_ETO₂) to the same extent (117 ± 2 mmHg), but P_aO₂ became reduced (from 102 ± 2 to 78 ± 2 and 81 ± 3 mmHg, respectively). As pH decreased during maximal exercise (7.14 ± 0.02 vs. 7.30 ± 0.02), S_aO₂ also became lower (92.9 ± 0.7 vs. 95.1 ± 0.1%) and arterial O₂ content (C_aO₂) was 202 ± 3 mL L^?1. An inspired O₂ fraction (F_IO₂) of 0.30 (n = 8) did not affect V_E, but increased P_ETO₂ and P_aO₂ to 175 ± 4 and 164 ± 5 mmHg and the P_ETO₂–P_aO₂ difference was reduced (21 ± 4 vs. 36 ± 4 mmHg). pH did not change when compared with normoxia and S_aO₂ remained within 1% of the level at rest in hyperoxia (99 ± 0.1%). Thus, C_aO₂ and VO _2max increased to 212 ± 3 mL L^?1 and 5.7 ± 0.2 L min^?1, respectively. The reduced P_aO₂ became of importance for S_aO₂ when a low pH inhibited the affinity of O₂ to haemoglobin. An increased F_IO₂ reduced the gradient over the alveolar-arterial membrane, maintained haemoglobin saturation despite the reduction in pH and resulted in increases of the arterial oxygen content and uptake.     

Effect of hyperoxia on maximal O2 uptake in exercise-induced arterial hypoxaemic subjects

This study focuses on the effect of hyperoxia on maximal oxygen uptake and maximal power (Pmax) in subjects exhibiting exercise-induced arterial hypoxemia (EIH) at sea level. Sixteen competing male cyclists >60 ml·min^–1·kg^–1) performed exhaustive ramp exercise (cycle-ergometer) under normoxia and moderate hyperoxia (FIO₂=30%). After the normoxic trial, the subjects were divided into those demonstrating EIH during exercise [arterial O₂ desaturation ( SaO₂) >5%; n=9] and those who did not (n=7). Under hyperoxia, SaO₂ raised and the increase was greater for the EIH than for the non-EIH group (P<0.001). improved for both groups and to a greater extent for EIH (12.8±5.7% vs. 4.2±4.6%, P<0.01; mean±SD) and the increase was correlated to the gain in SaO₂ for all subjects (r=0.71, P<0.01). Pmax improved by 3.3±3.3% (P<0.01) regardless of the group. These data suggest that pulmonary gas exchange contributes to a limitation in and power for especially EIH subjects.     

Changes in performance,maximal oxygen uptake and maximal accumulated oxygen deficit after 5, 10 and 15 days of live high:train low altitude exposure

Nineteen well-trained cyclists (14 males and 5 females, mean initial V˙O_2max 62.3 ml kg^–1 min^–1) completed a multistage cycle ergometer test to determine maximal mean power output in 4 min (MMPO_4min), maximal oxygen uptake (V˙O_2max) and maximal accumulated oxygen deficit (MAOD). The athletes were divided into three groups, each of which completed 5, 10 or 15 days of both a control condition (C) and live high:train low altitude exposure (LHTL). The C groups lived and trained at the ambient altitude of 610 m. The LHTL groups spent 8–10 h night^–1 in normobaric hypoxia at a simulated altitude of 2,650 m, and trained at the ambient altitude of 610 m. The changes to MMPO_4min, V˙O_2max and MAOD in response to LHTL altitude exposure were not significantly different for the 5-, 10- and 15-day treatment periods. For the pooled data from all three treatment periods, there were significant increases in MMPO_4min [mean (SD) 5.15 (0.83) W kg^–1 vs 5.34 (0.78) W kg^–1] and MAOD [50.1 (14.2) ml kg^–1 vs 54.9 (13.1) ml kg^–1] in the LHTL athletes between pre- and post-altitude exposure. There were no significant changes in MMPO_4min [5.09 (0.76) W kg^–1 vs 5.16 (0.86) W kg^–1] or MAOD [50.5 (14.1) ml kg^–1 vs 49.1 (13.0) ml kg^–1] in the C athletes over the corresponding period. There were significant increases in V˙O_2max in the athletes during both the LHTL [63.2 (9.0) ml kg^–1 min^–1 vs 64.1 (9.0) ml kg^–1 min^–1] and C [62.0 (8.6) ml kg^–1 min^–1 vs 63.4 (9.2) ml kg^–1 min^–1] conditions. In these athletes, there was no difference in the impact of 5, 10 or 15 days of LHTL on the increases observed in MMPO_4min, V˙O_2max or MAOD; and LHTL increased MMPO_4min and MAOD more than training at low altitude alone. Electronic Publication     

Maximal oxygen uptake,maximal voluntary isometric contraction and physical activity in young Danish adults

Summary The purpose of this study was to determine and compare interactions between the abdominal musculature and intea-abdominal pressure (IAP) during controlled dynamic and static trunk muscle loading. Myoelectric activity was recorded in six subjects from the rectus abdominis, obliquus externus, obliquus internus, transversus abdominis and erector spinae muscles using surface and intea-muscular fine-wire electrodes. The IAP was recorded intea-gastrically. Trunk flexions and extensions were performed lying on one side on a swivel table. An adjustable brake provided different friction loading conditions, while adding weights to an unbraked swivel table afforded various levels of inertial loading. During trunk extensions at all friction loads, IAP was elevated (1.8–7.2 kPa) with concomitant activity in transversus abdominis and obliquus internus muscles — little or no activity was seen from rectus abdomin is and obliquus externus muscles. For inertia loading during trunk extension, IAP levels were somewhat lower (1.8–5.6 kPa) and displayed a second peak when abdominal muscle activity occurred in the course of decelerating the movement. For single trunk flexions with friction loading, IAP was higher than that seen in extension conditions and increased with added resistance. For inertial loading during trunk flexion, IAP showed two peaks, the larger first peak matched peak forward acceleration and general abdominal muscle activation, while the second corresponded to peak deceleration and was accompanied by activity in transversus abdominis and erector spinae muscles. It was apparent that different loading strategies produced markedly different patterns of response in both trunk musculature and intea-abdominal pressure.     

Relationship between cardiac output and oxygen uptake at the onset of exercise

Summary The purpose of the present study was to assess the relationship between the rapidity of increased gas exchange (i.e. oxygen uptake ) and increased cardiac output ( ) during the transient phase following the onset of exercise. Five healthy male subjects performed multiple rest-exercise or light exercise (25 W)-exercise transitions on an electrically braked ergometer at exercise intensities of 50, 75, or 100 W for 6 min, respectively. Each transition was performed at least eight times for each load in random order. The was obtained by a breath-by-breath method, and was measured by an impedance method during normal breathing, using an ensemble average. On transitions from rest to exercise, rapidly increased during phase I with time constants of 6.8–7.3 s. The also showed a similar rapid increment with time constants of 6.0–6.8 s with an apparent increase in stroke volume (SV). In this phase I, increased to about 29.7%–34.1% of the steady-state value and increased to about 58.3%–87.0%. Thereafter, some 20 s after the onset of exercise a mono-exponential increase to steady-state occurred both in and with time constants of 26.7–32.3 and 23.7–34.4 s, respectively. The insignificant difference between and time constants in phase I and the abrupt increase in both and SV at the onset of exercise from rest provided further evidence for a cardiodynamic contribution to following the onset of exercise from rest.     

Effects of maximal effort strength training with different loads on dynamic strength, cross-sectional area, load-power and load-velocity relationships

The effects of maximal effort strength training with different loads on maximal strength, muscle cross-sectional area, the load-power and load-velocity relationship were investigated in the elbow flexors. Physical education students were matched into three groups; G90 (n?=?9) trained with a load of 90%, G35 (n?=?11) with 35%, and G15 (n?=?10) with 15% of 1RM (1 repetition maximum). Training consisted of three to five sets, performed three times a week for 9 weeks. Each set consisted of two, seven and ten repetitions in G90, G35 and G15, respectively. Training was performed with the nondominant arm, and the dominant arm served as control. The 1RM increased 15.2 (SD 4.5)% (P?P?P?P?P?P?r?=?0.93, P?r?=?0.73, P?相似文献