Nobuo Yasuda

Little change in markers of protein breakdown and oxidative stress in humans in immobilization- induced skeletal muscle atrophy

A number of studies in rodents suggest that disuse atrophy results from a large increase in proteolysis affected by, or accompanying, increased oxidative stress. Little information is available, however, about the effects of immobilization on markers of muscle protein breakdown and oxidative stress in humans. Therefore, the purpose of this investigation was to measure markers of breakdown or oxidative stress in subjects who underwent 14 days of knee-brace-mediated immobilization. Vastus lateralis samples taken from 21 young subjects before, and 2 days and 14 days after, single leg immobilization were measured for ubiquitin-protein conjugates, caspase 3/7 activity, the 14-kDa caspase-3 cleaved actin fragment, 4-hydroxy-2-nonenal (4-HNE) adducts, and protein carbonyls. Quadriceps cross-sectional area decreased by 5.7% +/- 1.1% (p < 0.0001) following immobilization. Ubiquitin-protein conjugates were elevated at 2 days of immobilization (12%, p < 0.05) but were not different from baseline at 14 days. Levels of the 14-kDa actin fragment and caspase 3/7 activity did not change over the immobilization period. The oxidative stress markers, 4-HNE adducts and protein carbonyls, did not change at any time point. These static measures of breakdown and oxidative modification suggest that a small increase in protein ubiquitination occurs early (2 days), but elevations in ubiquitinated or oxidatively modified proteins are not sustained during the later phase (14 days) of uncomplicated disuse atrophy in humans, suggesting that these pathways are not playing a major role in simple disuse-induced atrophic loss of protein mass.

Forced ventilation increases variability of isometric finger forces

The study aimed to assess the effects of forced ventilation on variability of the index finger force at the submaximal levels. Fourteen (6 men, 8 women) healthy subjects were instructed to perform self-initiated forced inspiration and forced expiration, the Valsalva maneuver and normal breathing while sustaining 15%, 30%, and 45% of maximal voluntary contraction (MVC) by the index finger. Standard deviation (S.D.) of finger forces increased significantly with the level of force. At each level of force, the mean force was not significantly changed under different breathing conditions. S.D. and coefficient variation (CV) during forced inspiration and expiration was significantly greater than S.D. and CV during normal breathing and the Valsalva maneuver at each force level. No significant differences in S.D. and CV were found between forced inspiration and expiration or between normal breathing and the Valsalva maneuver. Force variability synchronized with the initiation of forced inspiration and expiration, but not with the ventilation data during the Valsalva maneuver or normal breathing. These findings demonstrate clearly that finger force variability is affected by specific ventilation patterns at submaximal force levels. Therefore, assessment of force variability should consider the influence of ventilation.

No gender-specific differences in mechanical efficiency during arm or leg exercise relative to ventilatory threshold.

The purpose of this study was to determine economy and mechanical efficiency in men and women during both arm cranking (AC) and leg cycling (LC) at 70%, 85%, 100%, and 115% of mode‐specific ventilatory threshold (Tvent). Recreationally active men (n=9) and women (n=9) with similar values for %V̇O2peak at Tvent served as subjects. All subjects performed 5 min of exercise at each intensity of 70%, 85%, 100%, and 115% of Tvent for both AC and LC. Economy was expressed as W/L/min. Gross efficiency (GE) was determined as the ratio of work accomplished to total energy expended (%). Delta efficiency (DE) was determined as the ratio of delta work accomplished to delta energy expended (%). Economy and efficiency during LC were greater than during AC in men and women. During AC or LC exercise, no sex differences were found in either economy (P=0.93 for AC, 0.98 for LC), GE (P=0.88 for AC, 0.75 for LC), or DE (P=0.57 for AC, 0.51 for LC). These findings indicate that men and women show similar economy and efficiency during both AC and LC exercise when subjects have similar %V̇O2peak at Tvent.

Substrate oxidation during incremental arm and leg exercise in men and women matched for ventilatory threshold

Abstract The aim of this study was to determine the variations in substrate utilization between men and women matched for ventilatory threshold (T vent) during incremental arm cranking and leg cycling exercise at 70, 85, 100 and 115% of the mode-specific T vent. Recreationally active men (n = 12) and women (n = 10) with similar values for percentage of peak oxygen consumption at T vent participated in the study. Ventilatory equivalence, excess CO2 and modified V-slope methods were used concurrently to determine T vent. The participants performed 5 min of exercise at each of 70, 85, 100 and 115% T vent during both arm cranking and leg cycling exercise. The females were tested during the early follicular phase for all trials. A two-way mixed-design analysis of variance was performed to test for differences between the sexes. When carbohydrate and fat oxidation were expressed relative to total fat-free mass, carbohydrate oxidation during arm cranking and leg cycling was significantly higher in men than women at each percentage of T vent. In contrast, women showed significantly higher fat oxidation across intensities during both arm cranking and leg cycling. Our results suggest that when substrate utilization is expressed relative to total fat-free mass, women appear to maintain a higher rate of fat and lower rate of carbohydrate oxidation than men during both incremental arm cranking and leg cycling exercise relative to T vent.

Effects of repeated bouts of long-duration endurance exercise on muscle and urinary levels of 8-hydroxy-2ʹ-deoxyguanosine in moderately trained cyclists

Abstract The purpose of this study was to determine the effects of repeated bouts of long-duration endurance exercise on both muscle and urinary levels of oxidative DNA damage in moderately trained individuals. Seven moderately trained male cyclists participated in this study. All participants repeated two sessions consisting of a 5-h cycling period (equivalent to approximately 52%O2peak) followed by a 15-h rest, then a 40-km time trial. During the sessions, participants were instructed to take water ad libitum and to consume a standard sports drink consisting of 0.12 g·kg−1 body weight·hr−1 of carbohydrates. For each session, 24 h urine output was collected on the day before the 5-h exercise, and also between the 5-h exercise and 40-km time trial, in addition to between days 1–5 post-exercise. Subsequently, muscle and urinary levels of 8-hydroxy-2ʹ- deoxyguanosine (8-OHdG) were determined using high performance liquid chromatography with electrochemical detection. No significant alterations were observed between two sessions at the muscle or urinary levels of 8-OHdG. These results suggest that repeated bouts of exercise with a 7-day washout period may not lead to an accumulation of DNA damage products after a second 5-h stationary cycling bout.

Assessment of urinary protein composition in response to consecutive days of wildland firefighting

The purpose of this study was to examine the pattern of urinary protein excretion induced by 3 consecutive days of wildland firefighting. Eighteen male active-duty military personnel served as the participants. All testing on the 3 consecutive days was conducted at a Northwestern USA fire camp. All participants consumed military-based foods containing 2620–2864 kcal/day. The work activity was evaluated with an accelerometer in association with body weight and hydration markers over the experimental period. Urinary samples were collected pre and post workshift on days 1 and 3 to assess glomerular and tubular protein excretion (total protein, albumin, β2-microglobulin, N-acetyl-β-d-glucosaminidase and creatinine). The urinary levels of glomerular and tubular protein were not significantly different. The main findings of the present study indicate that similar alterations of urinary protein composition can be observed over consecutive days of wildland firefighting, which appears to be dependent on intensity rather than total work output.

SUBSTRATE UTILIZATION DURING ARM AND LEG EXERCISE RELATIVE TO THE VENTILATORY THRESHOLD IN MEN

BACKGROUND The purpose of this study was to determine variations in substrate utilization in men during arm and leg exercise at 70 and 90% of mode specific ventilatory threshold (Tvent). METHODS Ten males served as subjects. Limb total and muscle volumes were estimated in the right arm and leg with anthropometry. Ventilatory equivalence, excess CO2, and modified V-slope methods were used to determine Tvent. Subjects performed 15 min of exercise at 70 and 90%Tvent arm cranking (AC) exercise, and 70 and 90%Tvent leg cycling (LC) exercise. RESULTS VO2, VE, and HR were higher during LC exercise at both intensities. However, arm and leg RPE were not different at 70 and 90%Tvent. There were no significant differences between modes at 70%Tvent in relative carbohydrate use (54.5+/-9.5 and 57.8+/-8.2% for AC and LC, respectively) and relative fat oxidation (45.5+/-9.5 and 42.2+/-8.2% for AC and LC, respectively). However, at 90%Tvent, relative carbohydrate oxidation was significantly higher during AC versus LC exercise (75.4+/-10.6 versus 68.6+/-9.0%, p<0.05). Energy expenditure (total kJ x min(-1) was significantly lower during AC exercise (14.5+/-2.9 and 18.4+/-3.4 for the 70 and 90%Tvent, respectively) versus LC exercise (27.1+/-3.3 and 34.8+/-4.1 for the 70 and 90%Tvent, respectively; p<0.05). CONCLUSIONS These results indicate that substrate use during AC exercise is similar to LC exercise at 70%Tvent. However, as the exercise intensity increases, the smaller arm musculature becomes more dependent on carbohydrate utilization compared to the legs.