Effect of lactate consumption on exercise performance

BACKGROUND

Maintenance of plasma glucose is important in endurance performance. Gluconeogenesis or carbohydrate ingestion maintain glucose after hepatic glycogen depletion. Lactate may also serve as a gluconeogenic precursor as well as a blood buffer.

METHODS

To determine if an 8% carbohydrate (CHO) sports drink with and without a 2% lactate (L) solution increased endurance performance, peak power, and delayed blood acidosis, seven trained cyclists participated in a double-blind randomized study (6 males and 1 female) performed a bicycle test to determine max VO2max HR and the HR associated with the first respiratory exchange ratio (RER) value greater than 1.0 (target HR). Four bicycle rides to exhaustion, separated by one week, were done at a constant workload at a HR 10 beats below each subject's target HR. After a 12-hour fast, subjects received 100 g CHO 2-3 hrs before each test. Mean exercise heart rate was 86-87% max HR. During the final 30 s of each ride the Wingate power test was performed. Subjects consumed either (placebo, 2% L, 8% CHO or 8% CHO plus 2% L) every 20 min. Blood samples were collected before, every 30 min during and immediately following the test.

RESULTS

No significant differences were observed in total time (placebo: 95.3 +/- 25.8, 2% lactate: 95.7 +/- 30.0, 8% CHO: 105.2 +/- 37.2, 8% CHO + 2% lactate: 89.0 +/- 28.1 min) or peak power (placebo: 798.2 +/- 241.1, 2% L: 750.1 +/- 279.2, 8% CHO: 789.4 +/- 353.5, 8% CHO + 2% L: 716.3 +/- 331.3 Watts) among drinks. There were no differences in insulin, glucose, pH and HCO3- after the power tests among the drinks.

CONCLUSION

Exercise performance is unaffected by oral supplementation with lactate.

The effects of exercise intensity on body composition, weight loss, and dietary composition in women

OBJECTIVE

There is controversy over whether exercise and/or exercise intensity has an effect on total caloric intake or diet composition. The purpose of this study was to test the effect of exercise intensity without dietary manipulation on body composition and/or weight loss and to determine whether exercise intensity affected total caloric intake or diet composition in normal weight young women.

METHODS

Fifteen women aged 18 to 34 years with a maximal oxygen consumption average or below on the Palo Alto norms served as subjects. Subjects were randomly assigned to: 1) low heart rate intensity exercise group (LI, N = 7) which exercised 40 to 45 minutes approximately four times weekly at a mean heart rate of 132 beats per minute (bpm); 2) high heart rate intensity group (HI, N = 8) which exercised 40 to 45 minutes approximately four times weekly at a mean HR of 163 bpm. All subjects were given a maximal exercise test prior to and during weeks eight, 12 and 16. The first 4 weeks served as a control period, followed by approximately 11 weeks of exercise. Each subject recorded her dietary intake for 1 complete week, including a weekend, during weeks 2, 6, 10 and 14 of the study.

RESULTS

VO2 max increased (p < .05) in HI (29 +/- 6 ml/kg/minute to 38 +/- 7) but did not change in LI (36 +/- 5 to 38 +/- 7). Percent fat decreased in HI (p < .05) (27 +/- 7 to 22 +/- 4) but was unchanged in LI (22 +/- 6 to 21 +/- 6). The weekly intake of total kcal, carbohydrate, protein and fat did change significantly for either group. The weekly intake of saturated fat declined significantly (p < .05) in HI (21.2 +/- 5.8 g to 14.9 +/- 5.5 g); their weekly intake of cholesterol also decreased (p < .05) between months 2 to 3 (249 +/- 109 mg to 159 +/- 58 mg). No other differences in dietary intake between groups were found.

CONCLUSION

High heart rate intensity exercise training without dietary manipulation resulted in a decrease in body fat, but not weight change, as well as a decrease in the intake of saturated fat and cholesterol in normal weight young women. These changes were not observed after low heart rate intensity training.

Effect of low dose oral contraceptives on exercise performance

OBJECTIVE

to examine the effect of cycle phase or a low dose oral contraceptive on exercise performance in young women.

METHODS

As controls, 15 men were tested twice by a maximal treadmill test (Vo2 max) and by an endurance run 14 d apart to determine performance variability from causes other than hormonal fluctuations. Ten women ages 18-30 were then tested for Vo2 max and endurance in the same way in both the follicular and the luteal phase (random order, ovulation assessed by sonography). They were then randomly assigned to placebo (n = 3) or oral contraceptive (1 mg norethindrone and 35 micrograms ethinyl oestradiol) (n = 7) for 21 days. Tests were repeated during the first and third weeks of treatment. Vo2 max and endurance tests were compared in the men and control cycle of the women by using independent t tests on percent change. The data for both cycles in the women were analysed by repeated measures ANOVA.

RESULTS

There was no difference in per cent change in total test time, Vo2 max, or breathing frequency between the men and women in either test. Data obtained during the Vo2 max test revealed no difference between the follicular and luteal phases of the menstrual cycle for total test time [11.8 (SD 2.3) v 12.6 (2.3) min], Vo2 [41.6 (12.1) v 39.7 (11.4) ml.kg-1.min-1], or breathing frequency [26.8 (3.5) v 27.3 (9.9) breaths.min-1] respectively, or during the first and third weeks of treatment [total test time 12.0 (2.5) v 12.8 (2.4) min; Vo2 37.3 (7.4) v 41.0 (12.4) ml.kg-1.min-1; breathing frequency 27.8 (4.2) v 27.7 (3.4) breaths.min-1, respectively]. Data obtained during the endurance test revealed no difference between the follicular and luteal phase of the menstrual cycle for total test time [20.5 (15.7) v 16.2 (8.5) min], Vo2 [37.5 (9.4) v 32.9 (8.1) ml.kg-1.min-1], or breathing frequency [32.0 (6.0) v 33.2 (5.1) breaths.min-1, respectively], or during the first and third weeks of treatment [total test time 32.3 (34.9) v 30.6 (30.1) min; Vo2 33.9 (10.1) v 35.2 (8.6) ml.kg-1.min-1; breathing frequency 34.0 (5.9) v 34.8 (5.3) breaths.min-1, respectively].

CONCLUSIONS

Neither cycle phase nor a low dose oral contraceptive containing 1 mg norethindrone adversely affects performance during a maximal treadmill test or endurance run.

West Virginia physicians: cardiovascular risk factors, lifestyles and prescribing habits

Physicians educate their patients by direct teaching and by serving as a role model. Through the use of questionnaires, we evaluated the degree to which physicians in West Virginia participate in these activities. Thirty-five percent of the 2,404 licensed physicians in the state returned completed questionnaires. Although 90% prescribed appropriate diets and recommended exercise for their patients, the physicians who responded were often less likely to follow their own advice. Twenty percent of the male physicians and 13% of the female doctors were obese; 30% had LDL cholesterol levels over 130 mg./dl.; 13% had HDL cholesterol values of less than 35 mg./dl.; and 8% had triglycerides over 250 mg./dl. Participation in regular exercise (30 minutes three times per week) was reported by 48% of the male physicians and 47% of the female physicians. Eight percent of the men were smokers, as were 1.9% of the females. These results suggest that the role model aspect of patient education may need to be improved among some West Virginia physicians. It is an inexpensive method of directing attention to lifestyle in order to decrease preventable disorders such as coronary artery disease, obesity, diabetes, and hypertension.

Acute effects of laboratory stress on blood glucose in noninsulin-dependent diabetes

The acute effects of two psychological stressors (personally stressful imagery and threat of shock) on blood glucose (BG), heart rate, blood pressure, skin conductance, and subjective stress were studied in 22 noninsulin-dependent diabetic adults and nine healthy, nondiabetic subjects similar in age, weight, education and sex. The diabetic group's BG rose significantly after threat of shock (M change from rest = 18.4 mg/dL, p < .05), although the nondiabetic group's BG remained stable throughout the assessment. Significant increases in subjective stress ratings (p < .05) and skin conductance level (p < .05) paralleled the noninsulin-dependent diabetes mellitis (NIDDM) subjects' BG response to threat of shock. The findings suggest that some stressors can have hyperglycemic effects on individuals with NIDDM, although generalization of these findings to the natural environment remains to be demonstrated. The methodology used is contrasted with other studies that have failed to demonstrate stress effects on BG.

Hypertension and exercise. Where do we stand?

Several risk factors have been identified in patients with essential hypertension. The question is whether regular exercise programs can either prevent or alleviate elevated blood pressure. Published studies generally indicate that aerobic exercise of large-muscle groups can be used as an interventional regimen for hypertension. For mild hypertension, moderate-intensity walking is recommended at least three times a week. Improvement may not be evident in less than 6 months. When exercise alone is not effective or when hypertension is more severe, exercise can still be used as an adjunct to pharmacologic therapy.

Simulated swimming: a useful tool for evaluation the VO2 max of swimmers in the laboratory

This study was designed to develop a simulated swimming exercise (SS) so that peak VO2 would be assessed on swimmers in a laboratory setting. The subjects assumed a prone position on an incline bench and performed arm cranking on a Monark Rehab Trainer while performing a flutter kick against tension supplied by elastic cords. The SS test was compared to four peak VO2 tests: treadmill running (RN), tethered swimming (TW), bicycle ergometry (B), and arm cranking (AC). Eleven male varsity swimmers underwent each of the five VO2 max tests, and maximal cardiorespiratory indicators (HR, VE, VO2, O2 pulse, and RQ) were measured. The percentage of peak VO2 obtained during SS was compared to RN, TW, B, and AC. The SS test achieved 78 percent of RN, 91 percent of TW, 81 percent of B, and 124 percent of AC. There were no significant differences in VO2 in ml/kg.min between SS and TW. As expected, RN and B were significantly higher, while AC was lower. Ten subjects performed the SS test twice on two separate days within one week. The reliability of VO2 max in ml/kg.min was 0.95. the validity of VO2 max in ml/kg.min in the SS test vs. RN was 0.68. The SS test is reliable and can be used as effectively as TW to assess the VO2 max of swimmers in a laboratory setting.

Physical activity and condition, dietary habits, and serum lipids in second-year medical students

Level of physical activity has been found to be an independent risk factor for coronary heart disease. Because lifestyle and dietary habits are frequently established by early adulthood, we examined the physical activity, physical fitness, body composition, plasma lipids, and diets of a group of second-year medical students. Medical students were studied because of the presumption that they were knowledgeable about exercise and appropriate diet and would have future influence on their patients. A questionnaire which assessed physical activity was returned by 69 (89%) of the 80 students. Over 50% reported no hard or very hard physical activity either during the week or on weekends. Three subjects were smokers. Body composition, cardiovascular fitness, and plasma lipids were assessed in 20 subjects selected at random from the 69. Five of the 15 men, but none of the five women, had greater-than-desirable body fat. Cardiovascular fitness was at least average compared to normal values, but three had hypertension at rest and 12 had hypertensive responses to exercise. Seven of the men had LDL cholesterol above 130 mg/dl and three had LDL:HDL ratios greater than 3. There was a positive correlation (r = 0.5, p = 0.02) between hard/very hard activity assessed by questionnaire and VO2max and a negative correlation (r = 0.4, p = 0.05) between VO2max and percent fat. All 20 subjects reported above average to severe amounts of stress. Analysis of a 48-hr diet record of 22 students showed an average consumption of 47% carbohydrates, 17% protein, and 36% fat. The polyunsaturated/saturated ratio was 0.43.(ABSTRACT TRUNCATED AT 250 WORDS)

Coronary risk factors in type II diabetes: response to low-intensity aerobic exercise

Patients with non-insulin-dependent diabetes are at greatly increased risk for coronary artery disease. Although exercise training has been shown to decrease risk factors, the presence of obesity, older age, and a sedentary lifestyle make a high-intensity exercise program an unrealistic choice of therapy. Therefore, we examined the effect of a low-to-moderate-intensity (mean 69 per cent of maximal heart rate) walking program on lipids, glucose, insulin, glycosylated hemoglobin and cardiovascular fitness. Nine women and seven men, mean age 56, were randomly assigned to a control or an exercise group which exercised three times per week for two months. Supervised exercise sessions consisted of 40-45 minutes of walking and/or slow jogging. Subjects continued on their usual diets. The trained group showed a significant improvement in VO2max from 1.65 to 1.95 L/min. Resting systolic blood pressure decreased from 141 to 130 mm Hg after training, and resting heart rate decreased from 88 to 81. Glycosylated hemoglobin decreased in the exercise group in seven or eight subjects and in only two of eight controls. Triglycerides decreased in the exercise group from 285 to 223 mg/dl. Body weight, total and HDL cholesterol, glucose, and insulin did not change in either group. These data indicate that a low-to-moderate level of aerobic training, independent of dietary changes, is an effective and feasible method of improving cardiovascular risk factors: physical fitness, systolic blood pressure, plasma triglycerides, and glycemic control in non-insulin-dependent diabetic subjects.

Combined effects of aerobic exercise and omega-3 fatty acids in hyperlipidemic persons

Because both aerobic exercise and fish oil ingestion have been shown to decrease plasma lipids, we examined the effects of combining these modalities in hyperlipidemic subjects. Thirty-four subjects were randomly assigned to one of four groups as follows: fish oil and exercise (FE), N = 7, 50 ml of oil daily and 3 d.wk-1 of aerobic exercise; fish oil (F), N = 7, 50 ml of oil daily; corn oil (CN), N = 10, 50 ml of oil daily; and control (C), N = 10. Blood samples were drawn at baseline and at the end of 4, 8, and 12 wk. The FE and F groups showed significantly lower triglycerides with respect to treatment as compared to the CN and C groups. The FE, F, and CN groups exhibited lower total cholesterol values than the control group but were not different from each other. HDL cholesterol was significantly increased after treatment in the FE and F groups as compared to the CN and C groups. Serum apo-B, LDL cholesterol, and LDL protein decreased significantly in the FE group but not the F group from baseline to 12 wk. VO2max increased and percent fat decreased only in the FE group. In conclusion, aerobic exercise improved the effects of fish oil on LDL cholesterol and apo-B and improved fitness and body composition in hyperlipidemic subjects.

Increased HDL-cholesterol levels with a weight lifting program

Weight training regimens are generally thought not to improve cardiovascular function or lipid parameters. To evaluate this further, we studied 25 men before and after supervised weight training three times each week for eight weeks. Mean plasma HDL-cholesterol level increased significantly with training, from 38.8 to 44.1 plasma HDL-cholesterol level increased significantly with training, from 38.8 to 44.1 mg/dl, while calculated LDL-cholesterol decreased from 132 to 121 mg/dl. Triglyceride values were unchanged. Percent fat decreased from 14% to 12.7% (P less than .05), and muscle mass increased from 32.4 kg before training to 37 kg after training (P less than .05). Maximal oxygen consumption (VO2max) increased significantly (from 45.2 to 49.2 ml/kg X min) during the eight-week period. LDL-cholesterol and triglycerides were negatively correlated with VO2max but changes in HDL-cholesterol were not accounted for by alterations in VO2max, muscle mass, or percent fat. This study suggests that weight training can be used to increase strength, alter body composition, improve plasma lipids, and enhance cardiovascular function.

Weight training and strength, cardiorespiratory functioning and body composition of men

Forty-five men (18-35 years) trained three times a week for eight weeks to determine the effects of four constant-resistant weight training programmes on muscular strength, endurance, body composition and cardiovascular functioning. Subjects were randomly assigned to one of four programmes: Endurance (2 sets of 15 repetition maximum [RM]); Explosive (1 set of 15 RM); Strength 1 (3 sets of 6 RM); Strength 2 (1 set of 10 RM twice weekly and 1 set of 3 RM once weekly). All groups showed significant increases in elbow and shoulder flexion strength with elbow extension strength improved in the Explosive, Strength 2 and Endurance groups. Shoulder extension strength improved the Endurance group and in the Strength 2 group. Maximum oxygen uptake (L/min) and (ml X kg-1 min-1) improved significantly in the Endurance and Strength 2 groups. Lean body weight increased significantly in all groups except the Strength 1 group, but there was no change in % fat for any group. Due to a high drop out rate (55%) and injury related problems, the Explosive technique is not recommended. The Endurance and Strength 2 programmes were most effective for improving physiologic functioning, as assessed in this study.

The effects of exercise on the bones of postmenopausal women

The effects of walking and aerobic dancing on the bones of 73 recently postmenopausal women have been compared by photon absorptiometry of the distal radius with a control group who did not exercise. The period of observation was six months. Results showed that the control group and the walking group lost statistically significant amounts of bone mineral content (1.6%, and 1.7% respectively), but that the dancing group did not (0.8%). The control group did not show a significant increase in the bone width (0.9%), but both the dancing (1.3%) and walking (1.6%) groups did. Changes in the cross-sectional moment of inertia of the radius were estimated for each subject based on bone mineral content and bone width values. Both exercise groups experienced significant increases in this variable, while the control group did not. Plasma oestrogen levels were not influenced by exercise. The results support the hypothesis that mechanical loading due to exercise may be effective in preventing postmenopausal osteoporosis.

Senile osteoporosis. The effects of exercise

The available literature indicates that a high level of physical activity throughout life can result in increased skeletal mass during the fourth decade. Such a large reservoir of bone mass at midlife may delay the clinical manifestations of osteoporosis in later life. Furthermore, the published studies of animal models and humans strongly suggest that physical activity retards or prevents involutional bone loss in both recently postmenopausal and very elderly women.