Effect of High-Intensity Resistance Exercise on Elderly Bones; Exercise Intensity and Fat Oxidation; Complex vs. Simple Carbohydrates for Metabolic Syndrome.
Vincent, K.R., & Braith, R.W. Resistance exercise and bone turnover in elderly men and women. Medicine & Science in Sports & Exercise, 34 (1), 17-23.
Study. Researchers at the University of Florida at Gainesville examined the effects of six months of high- or low-intensity resistance exercise (REX) on bone mineral density (BMD) and biochemical markers of bone turnover in adults ages 60 to 83 years. Sixty-two men and women (average age = 68.4 years) were stratified for strength and randomly assigned to a control group (CON, n = 16), a low-intensity group (LEX, n = 24) or a high-intensity group (HEX, n = 22). All subjects were free from orthopedic and cardiovascular problems at baseline.
The REX training—performed on MedX® resistance machines—was progressive. The two active groups completed one set of each of the following exercises: abdominal crunch, leg press, leg extension, leg curl, calf press, seated row, chest press, overhead press, biceps curl, seated dip, lumbar extension, leg abduction and leg adduction. Subjects trained at either 50 percent of one-repetition maximum (1 RM) for 13 repetitions (LEX) or 80 percent of 1 RM for eight repetitions (HEX) three times per week for 24 weeks. Vincent and Braith determined each subject’s 1 RM for eight of those exercises at baseline and at the end of the study. BMD was measured for total body, femoral neck and lumbar spine using dual-energy X-ray absorptiometry. The researchers also measured serum levels of osteocalcin, bone-specific alkaline phosphatase (BAP) and pyridinoline cross-links (PYD) (all markers of bone generation).
By the end of the training program, both the active groups had significantly increased their 1 RM for all exercises tested (p ≤ 0.05). The percent increases in total strength (sum of all eight 1 RMs) equaled 17.2 percent for the LEX group and 17.8 percent for the HEX group. BMD of the femoral neck increased significantly (+1.96%, p < 0.05) for the HEX group. There were no other significant changes in BMD. Osteocalcin increased by 25.1 and 39.0 percent for the LEX and HEX groups, respectively (p < 0.05). BAP increased significantly (+7.1%, p < 0.05) for the HEX group. From these data, Vincent and Braith concluded that high-intensity REX training improved BMD of the femoral neck in healthy elderly subjects. The findings also suggested that REX training increased bone turnover, which over time might lead to further changes in BMD.
Comments. One of the striking findings of this study was that a one-set exercise stimulus, executed three times per week, significantly increased regional (femoral neck) BMD in healthy elderly persons. The investigators hypothesized that greater improvements in BMD might have occurred in other anatomic regions (e.g., the spine), had the program lasted longer than six months. The fact that these subjects were healthy and had normal BMD at baseline may have limited further increases in bone mineral content. Given past research findings, it is doubtful whether an additional set would have influenced the outcome. It is possible that multiple sets (3 or 4) would have resulted in bigger gains; however, such lengthy exercise sessions might have been time prohibitive for this population.
Achten, J., Gleeson, M., & Jeukendrup, A.E. 2002. Determination of the exercise intensity that elicits maximal fat oxidation. Medicine & Science in Sports & Exercise, 34 (1), 92-7.
Study. Exercise physiologists at the University of Birmingham in Birmingham, England, attempted to develop a test protocol to determine the exercise intensity at which fat oxidation rate is maximal (Fatmax). Eighteen moderately trained cyclists (average age = 28 years) performed to exhaustion a graded exercise test (GE35/5) in which the work rate increased by 35 Watts (W) every five minutes until the respiratory exchange rate reached 1.0, after which the work rate increased by 35 W every two minutes. Subjects also performed—on separate days—four to six continuous, prolonged exercise tests (CE) at constant work rates, corresponding to the work rates of the GE test. The duration of each test was chosen so that all exercise test trials would result in an equal energy expenditure. Seven other subjects were asked to perform three different GE tests to exhaustion: GE35/5, GE35/3 (in which the work rate increased by 35 W every 3 minutes) and GE20/3 (in which the work rate increased by 20 W every 3 minutes). The investigators measured fat oxidation using indirect calorimetry (i.e., equations predicting fat and carbohydrate utilization from VO2 and VCO2 measurements).
The authors found that Fatmax determined with the GE35/5, average fat oxidation in the CE tests and fat oxidation measured during the first five minutes of the CE tests were not significantly different (56%, 64% and 58% of VO2max, respectively). Results of the GE35/5 protocol were used to construct an “exercise intensity vs. fat oxidation” curve for each individual. Fatmax was equivalent to 64 percent of VO2max and 74 percent of heart rate maximum (HRmax). The Fatmax zone (the range of intensities with fat oxidation rates within 10% of the peak rate) was located between 55 and 72 percent of VO2max. The contribution of fat oxidation to energy expenditure became negligible above 89 ± 3 percent of VO2max (92 ± 1% of HRmax). When stage duration dropped from five to three minutes or when increment size dropped from 35 to 20 W, no significant differences were found in Fatmax, the Fatmax zone or the minimum fat oxidation rate.
The research team concluded that an exercise test protocol with three-minute stages and 35-W increments in work rate could be used to determine Fatmax. They found that fat oxidation rates were high over a large range of exercise intensities, but at intensities above Fatmax levels, fat oxidation rates dropped markedly.
Comments. Although most fitness professionals will not be in a position to construct tests to assess maximum metabolic response, this study did confirm one clear outcome: In moderately trained men, average age 28 years, fat oxidation rates appeared to be high over a large range of exercise intensities, namely 55 to 72 percent of VO2max. This is an important concept to grasp for those who still adhere to the misconception that the “fat-burning zone” is confined to a narrow and limited exercise intensity range. Fitness professionals must also be cautious and avoid the erroneous inference that weight loss will result only in those who exercise within the Fatmax zone. While it is certainly true that exercising within the range of intensities defined in this study as the Fatmax zone may be the most efficient way to sustain caloric expenditure, fat weight loss itself is best predicted by total caloric expenditure (expenditure during the exercise session plus recovery time).
Poppitt, S.D., et al. 2001. Long-term effects of ad libitum low-fat, high-carbohydrate diets on body weight and serum lipids in overweight subjects with metabolic syndrome. American Journal of Clinical Nutrition, 75, 11-20.
Overweight individuals with metabolic syndrome are at increased risk of type 2 diabetes and coronary vascular disease. Dietary intervention may ameliorate weight gain and other features of the syndrome. Researchers in England and New Zealand collaborated to investigate what effect it would have on body weight and intermediary metabolism if subjects replaced one-quarter of their daily fat intake with complex or simple carbohydrates.
Forty-six subjects with at least three risk factors for metabolic syndrome were randomly assigned to receive a control diet; a low-fat, complex-carbohydrate diet (LF-CC); or a low-fat, simple-carbohydrate diet (LF-SC) for six months. Thirty-nine subjects completed the trial. About 60 percent of daily dietary intake was provided free of charge through a grocery store. The dietary goals were as follows:
1. Keep fat intake at 35 to 40 percent of total calories in the control group.
2. Reduce fat intake by 10 percent of total calories in both low-fat groups.
3. Alter the ratio of simple to complex carbohydrates to 1:2 in the LF-CC group.
4. Alter the ratio of simple to complex carbohydrates to 2:1 in the LF-SC group.
Energy intake was ad libitum; in other words, participants were allowed to eat as much as they wished. Poppitt and associates measured the subjects’ body weight, body mass index, blood pressure and blood lipids at months 0, 2, 4 and 6.
Weight loss was greatest with the LF-CC diet. The controls gained an average of 1.03 kilograms (kg) (not a significant change); subjects on the LF-CC diet lost an average of 4.25 kg (p < 0.01); and those on the LF-SC diet lost an average of 0.28 kg (not a significant change). Total cholesterol decreased by 0.33 millimoles per liter (mmol/L), 0.63 mmol/L and 0.06 mmol/L in subjects consuming the control, LF-CC and LF-SC diets, respectively (difference between the LF-CC and LF-SC groups: p < 0.05). There were no significant changes in LDL cholesterol, whereas HDL cholesterol decreased over time in all three groups (p < 0.0001). Triglyceride concentrations were higher in the LF-SC group than in the other two groups (p < 0.05). A low-fat, high-polysaccharide diet in overweight individuals with abnormal intermediary metabolism led to moderate weight loss and some improvement in serum cholesterol. Increasing simple carbohydrates did not promote weight gain, but nor did this intervention improve body weight or lipid profile.
Comments. Metabolic syndrome, as defined by the National Institutes of Health (National Cholesterol Education Program Adult Treatment Panel III report), is characterized by having three or more of the following metabolic risk factors: excess abdominal fat; triglycerides > 150 milligrams per deciliter (mg/dl); HDL cholesterol < 40 mg/dl in men, < 50 mg/dl in women; borderline or stage I hypertension; and fasting glucose 110 to 125 mg/dl. The syndrome is very prevalent in the United States. In fact, recent reports estimate that over 40 percent of men and women 50 to 60 years of age have it. The importance of this statistic is that people with a cluster of metabolic risk factors are at high risk for diabetes and cardiovascular disease. The present study demonstrates that people with metabolic syndrome can achieve significant weight loss and reduce their total cholesterol concentrations by replacing 25 percent of their dietary fat with complex carbohydrates. Replacing the same amount of fat with simple carbohydrates resulted in measurable, but not significant, weight loss. Regarding the drop in subjects’ HDL cholesterol levels, diets high in carbohydrates and polyunsaturated fats do sometimes cause decreases in HDL levels; however, readers should not assume this means carbohydrates and polyunsaturated fats are bad. Clearly, adding 1,000 to 1,500 kilocalories of exercise per week to this dietary regimen would have generated greater weight reductions, lower triglycerides and higher HDL cholesterol levels. Metabolic syndrome presents one of the most important opportunities for fitness professionals (especially personal trainers and clinical exercise specialists) to partner with health care professionals (particularly diabetes care and lipid clinic teams).
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