Oxygen Consumption Of Subjects Research Articles

Patients with Type 1 Diabetes Oxidize Fat at a Greater Rate than Age– and Sex–Matched Controls

Introduction: Elevated patient blood glucose and exogenous insulin administration may affect substrate oxidation in patients with type 1 diabetes mellitus (T1DM); however, this has not been demonstrated with conviction. We examined substrate oxidation during incremental exercise in a group of subjects with T1DM and compared the results to those of an age-and sex-matched control group of subjects. Methods: A group of subjects with T1DM (n=29; 10 men, 19 women) was recruited for metabolic testing from a weeklong fitness camp. An age- and sex-matched control group of subjects (n = 29; 10 men, 19 women) was recruited from the local community. Subjects were required to avoid strenuous exercise for 48 hours and fast for 2 hours prior to metabolic testing. An incremental test to exhaustion on either a stationary cycle or treadmill was administered to all subjects. Maximum oxygen consumption of subjects was measured (T1DM subjects: 41.4 ± 1.9 mL/kg/min; control subjects: 48.4 ± 1.3 mL/kg/min). Blood glucose was recorded at 20 and 5 minutes before the exercise test, and at 5 and 20 minutes after the exercise test. Results: The T1DM and control subjects were matched for age, height, weight, and body composition. Subject blood glucose levels were higher in the group of subjects with T1DM than the control group at all times measured (P < 0.001). At all relative intensities of exercise (50%-80% maximum oxygen consumption; P < 0.050), absolute fat oxidation was higher in the group of subjects with T1DM (P < 0.050) and absolute carbohydrate oxidation was higher in the control group. Conclusion: Our data indicate that subjects with T1DM oxidize fat at a higher rate and carbohydrates at a lower rate when compared with age- and sex-matched controls at the same relative intensity of exercise, despite the elevated pre-exercise blood glucose of subjects with T1DM.

Energy Expenditure, Cardiorespiratory, and Perceptual Responses to Shallow-Water Aquatic Exercise in Young Adult Women

Introduction: Aquatic exercise (AE) is a popular form of physical activity, yet few studies have assessed the individual's energy expenditure (EE) associated with a continuous bout of AE. Studies using indirect calorimetry to measure EE have reported limitations associated with test methodology and the ability to control individual's exercise intensity or tempo. Purpose: To evaluate EE and cardiorespiratory (CR) responses during a 40-minute shallow-water AE session in young adult women. Methods: Twenty-one healthy women (aged 21.7 ± 3.4 years) completed an orientation practice session and a 40-minute shallow-water AE session using a traditional exercise class format and the SWEAT video-based instructional cuing program. The high-intensity interval format included the following segments: 1) warm-up (3 minutes); 2) CR segment (22 minutes); 3) muscular endurance segment (ME; 10 minutes); and 4) cool-down (5 minutes). Subject oxygen consumption (VO2; mL/kg/min), heart rate (HR) and OMNI overall ratings of perceived exertion (RPE-O) were assessed each minute. Average kcal/min1, metabolic equivalents (METs; 1 MET = 3.5 mL/kg/min), and total kcals per segment and for the overall session were calculated. Results: The total subject EE throughout the 40-minute trial (including warm-up and cool-down segments) was 264 kcals, with an overall average of 6.3 kcals/min (5.6 METs). The average kcals/min expended throughout CR segments 2 through 6 was 8.05 (7.1 METs), with the Hoverjog segment producing the greatest average kcals/min at 8.3 (7.3 METs). The CR portion (22 min) contributed 65% of the total EE (171 kcals) of the 40-minute AE trial. For the overall AE trial, the highest and average subject VO2 achieved were 33.3 and 19.7 mL/kg/min, respectively. The average highest subject heart rate achieved was 177 beats per minute (bpm), equivalent to 90% of the participant's age-predicted HRmax. Conclusion: Energy expenditure during a 40-minute AE session met national recommendations for a daily moderate-to-vigorous bout of physical activity offering a viable alternative to land-based exercise. Because AE serves as a partial-weight bearing modality, future studies are needed to clarify the EE of shallow-water AE in apparently healthy and clinical populations.

Modeling effects of sagittal-plane hip joint stiffness on reciprocating gait orthosis-assisted gait

Upright ambulation is believed to improve quality of life for persons with lower-limb paralysis (LLP). However, ambulatory orthoses for persons with LLP, like reciprocating gait orthoses (RGOs), result in a slow, exhausting gait. Increasing the hip joint stiffness of these devices may improve the efficiency of RGO-assisted gait. The small, diverse population of RGO users makes subject recruitment challenging for clinical investigations. Therefore, we developed a lower-limb paralysis simulator (LLPS) that enabled nondisabled persons to exhibit characteristics of RGO-assisted gait, thereby serving as surrogate models for research. For this study, tests were conducted to determine the effects of increased hip joint stiffness on gait of nondisabled persons walking with the LLPS. A motion capture system, force plates, and spirometer were used to measure the hip flexion, crutch ground reaction forces (GRFs), and oxygen consumption of subjects as they walked with four different hip joint stiffness settings. Increasing the hip joint stiffness decreased hip flexion during ambulation but did not appear to affect the crutch GRFs. Walking speed was observed to initially increase with increases in hip joint stiffness, and then decrease. These findings suggest that increasing hip joint stiffness may increase walking speed for RGO users.

Measurement of Functional Capacity Requirements to Aid in Development of an Occupation-Specific Rehabilitation Training Program to Help Firefighters With Cardiac Disease Safely Return to Work

We designed a study to measure the functional capacity requirements of firefighters to aid in the development of an occupation-specific training program in cardiac rehabilitation; 23 healthy male firefighters with no history of heart disease completed a fire and rescue obstacle course that simulated 7 common firefighting tasks. They wore complete personal protective equipment and portable metabolic instruments that included a data collection mask. We monitored each subject's oxygen consumption (VO(2)) and working heart rate, then calculated age-predicted maximum heart rates (220 - age) and training target heart rates (85% of age-predicted maximum heart rate). During performance of the obstacle course, the subjects' mean working heart rates and peak heart rates were higher than the calculated training target heart rates (t(22) = 5.69 [working vs target, p <0.001] and t(22) = 15.14 [peak vs target, p <0.001]). These findings, with mean results for peak VO(2) (3,447 ml/min) and metabolic equivalents (11.9 METs), show that our subjects' functional capacity greatly exceeded that typically attained by patients in traditional cardiac rehabilitation programs (5 to 8 METs). In conclusion, our results indicate the need for intense, occupation-specific cardiac rehabilitation training that will help firefighters safely return to work after a cardiac event.

Regular walking increases peak limb vasodilatory capacity of older hypertensive humans: implications for arterial structure.

Although regular aerobic exercise has been shown to lower arterial blood pressure in older adult humans with essential hypertension, the mechanisms responsible for this hypotensive effect remain largely unknown. To examine the hypothesis that the reduction in arterial blood pressure in older hypertensive humans with regular exercise is accompanied by evidence of a change in arterial structure. We measured peak limb vascular conductance, a well-established noninvasive measure of arterial structure, both in the forearm (untrained limb) and in the calf (exercise-trained limb) of 22 older adults (aged 51-74 years) with stage 1 or 2 essential hypertension. Eleven subjects walked 3-4 days/week at a mild exercise intensity (45% of heart rate reserve) for 6 months. Eleven other subjects served as nonexercising controls. Maximal oxygen consumption of subjects in the exercise group increased by 17% (P < 0.05) with no change in body mass and body fat. Systolic and diastolic arterial blood pressures at rest were reduced by 7 +/- 4 and 5 +/- 2 mmHg, respectively (P < 0.05). There were roughly 20% increases in peak forearm blood flow and peak forearm vascular conductance (both P < 0.05). Similar increases in peak calf blood flow and vascular conductance were observed (both P < 0.01). There were no significant changes in any of these variables over the same time period for the nonexercising controls. The decrease in resting blood pressure in older adults with stage 1 or 2 essential hypertension in response to regular aerobic exercise is associated with an increase in peak limb vascular conductance, which could be due in part to favorable changes in arterial structure. These exercise-induced functional and, possibly, structural changes are not confined to the exercise-trained limbs, but rather are more systemic in nature. These apparent beneficial changes in limb vasodilatory capacity and vascular structure can be produced with a mode, intensity, and frequency of aerobic exercise that can be tolerated and is commonly performed by older adults.

Speculation on posture, locomotion, energy consumption, and blood flow in early hominids

Energy consumption and blood flow allocations were studied in human subjects who were induced to stand and walk in a bent-head, bent-knee way, which is one of the different bipedal behaviours that could be considered for the posture and locomotion of Australopithecus afarensis. In these subjects oxygen consumption was intermediate between modern humans standing/walking normally and humans standing/walking on all fours, and blood flow was lower for the internal carotid and subclavian arteries and higher for the external carotid and femoral arteries. When erect posture is similar to that of modern humans the demands of blood supply required by the general musculature are diminished in view of the relatively efficient modes of human posture and locomotion, but blood flow to the enlarged human brain is markedly increased.

Heart rate response to isocapnic hypoxia in conscious man.

We studied the effect of acute progressive hypoxia on heart rate in conscious healthy subjects. The PCO2 was held constant (+/- 1.5 mmHg) midway between the resting end-tidal and mixed-venous levels. Hypoxia was induced by having the subject rebreathe from a small bag so that the PO2 fell at a rate related to the subject's oxygen consumption. Arterial oxygen saturation (Sao2) was measured continuously during the procedure with an ear oximeter. We found that heart rate (HR) was best fitted to an inverse linear relation to arterial oxygen saturation and a power relation to PO2. The range of deltaHR/deltaSao2 was 0.62-1.46 beats/min per 1% fall in Sao2 (mean +/- SE = 0.98 +/- 0.06). There was no relationship between heart rate and ventilatory responses to hypoxia.