Background: Resistance training (RT) improves muscle strength and overall physical function in older adults. RT may be particularly important in the obese elderly who have compromised muscle function. Whether caloric restriction (CR) acts synergistically with RT to enhance function is unknown.
Objective: As the primary goal of the Improving Muscle for Functional Independence Trial (I’M FIT), we determined the effects of adding CR for weight loss on muscle and physical function responses to RT in older overweight and obese adults.
Design: I’M FIT was a 5-mo trial in 126 older (65–79 y) overweight and obese men and women who were randomly assigned to a progressive, 3-d/wk, moderate-intensity RT intervention with a weight-loss intervention (RT+CR) or without a weight-loss intervention (RT). The primary outcome was maximal knee extensor strength; secondary outcomes were muscle power and quality, overall physical function, and total body and thigh compositions.
Results: Body mass decreased in the RT+CR group but not in the RT group. Fat mass, percentage of fat, and all thigh fat volumes decreased in both groups, but only the RT+CR group lost lean mass. Adjusted postintervention body- and thigh-composition measures were all lower with RT+CR except intermuscular adipose tissue (IMAT). Knee strength, power, and quality and the 4-m gait speed increased similarly in both groups. Adjusted postintervention means for a 400-m walk time and self-reported disability were better with RT+CR with no group differences in other functional measures, including knee strength. Participants with a lower percentage of fat and IMAT at baseline exhibited a greater improvement in the 400-m walk and knee strength and power.
Conclusions: RT improved body composition (including reducing IMAT) and muscle strength and physical function in obese elderly, but those with higher initial adiposity experienced less improvement. The addition of CR during RT improves mobility and does not compromise other functional adaptations to RT. These findings support the incorporation of RT into obesity treatments for this population regardless of whether CR is part of the treatment.
Alex’s Notes: There is a disconnect between changes in muscle mass and muscle strength with aging, as exemplified by the Health ABC study in which age-related decline in muscle strength was reported to be two- to five-fold greater than the loss of muscle mass in adults aged 70–79 years over a 3-year follow-up. This suggests that there are other factors related to muscle quality that contribute to age-related declines of muscle function and mobility.
One such “other factor” may be adiposity, which has been shown to be inversely related to muscle strength and quality. Research suggests that greater intermuscular adipose tissue (IMAT) is associated with lower muscle strength and power and reduced physical functioning. This is concerning because 35.4% of adults ≥60 years are obese, a disease state characterized in part by excessive fat accumulation around [subcutaneous adipose tissue (SAT)] and within (IMAT) skeletal muscle.
Currently, participation in resistance exercise training is the only therapy known to consistently improve muscle mass, strength, power, and quality and overall physical function in older adults. Nonetheless, some research suggests that excess adiposity may limit the magnitude of improvement. For instance, despite similar muscle gain among younger normal-weight and overweight-obese individuals, the overweight-obese persons gained significantly less strength. A study of older adults confirmed these findings by showing that the muscle strength only improved in persons with a low baseline IMAT after undergoing a 12-week combined resistance, endurance, and balance training intervention.
This brings us to the goal of the study at hand: to determine whether fat loss during resistance training improves muscular adaptations to the training. In the end, 111 habitually sedentary, overweight-obese men and women aged 65-79 years completed a five-month resistance training program with (RT+CR) or without (RT) caloric restriction to induce weight loss. Body composition, quadriceps strength, power, & quality, and physical function and mobility were assessed at baseline and after the intervention.
The training was a standard machine-based program performed three times per week, consisting of 1) leg press, 2) leg extension, 3) seated leg curl, 4) seated calf, 5) incline press, 6) compound row, 7) triceps press, and 8) bicep curl. With a rest of ~1 minute between sets, the training goal was to complete 3 sets of 10 repetitions for each exercise. When a participant was able to complete 10 repetitions on the third set for 2 consecutive sessions at a certain weight, the weight was increased.
Participants assigned to RT only were instructed to follow a eucaloric diet, whereas those assigned to RT+CR underwent a dietary weight-loss intervention incorporating meal replacements, nutrition education, and dietary behavior modification advice via weekly meetings with the study’s registered dietitian. Each participant was assigned a daily caloric intake of 600 kcal below estimated maintenance requirements and provided with two meal replacement shakes for breakfast and lunch. Food logs were used to monitor compliance.
What happens to fat old people who lift?
On average, body weight and LBM were unchanged in the RT group, but there was huge inter-individual variation among the participants, with the changes in body weight ranging from -6 kg to +4.4 kg. This level of variation was present for changes in body fat as well, but on average there was a statistically significant loss of 0.6% body fat through significant reductions in both SAT and IMAT. Additionally, thigh muscle volume increased while thigh fat volume decreased.
Quadriceps strength, power, and quality (strength per unit of mass) all increased by the end of the intervention, as to be expected by a resistance training program. Similarly, physical performance as measured by a standing balance test, usual gait speed over a 4-m course, and time to complete five repeated chair rises with arms folded across the chest was significantly improved. However, mobility as measured through a 400-m walk time test was unchanged, as was self-reported disability and grip strength.
And when we throw a diet in the mix?
Everything that occurred in the RT group also occurred in the RT+CR group and then some. The magnitude of the changes was also significantly more pronounced. For instance, as per study design, weight loss averaged 4.9 kg or about 5.67% of the initial body weight, but the inter-individual range was from -12.6 kg to +4.1 kg. Fat loss was also six times greater than the RT group, averaging 3.6 kg, again through reductions in SAT and IMAT. Unfortunately, all this weight loss took its toll on LBM and resulted in a reduction of 1.1 kg (~26.9% of the total weight loss) and prevention in the gain of thigh muscle volume. Additionally, the change in IMAT was not different between the groups, suggesting that reductions are more dependent on lifting weights than weight loss.
The RT+CR group also showed improvement in every measure of physical function. The improvements in muscle strength, power, and quality and physical performance were not different from the RT group, but grip strength and quality (grip strength per unit of body mass) were significantly improved compared to baseline and compared to the RT group. Additionally, mobility and self-reported disability improved, suggesting these measures of physical function to be most dependent on weight loss.
To help illuminate the relationships between body composition and physical function, the researchers performed correlational analyses. Surprisingly, none of the changes in muscle-function measures correlated with initial LBM. Rather, individuals with a lower percentage of total body fat and less IMAT at baseline exhibited greater improvement in mobility, physical performance, and muscle strength and power in response to the resistance training intervention.
Further analyses were then performed to see how changes during the intervention were related. Again, changes in LBM or thigh muscle volume were not related to any other variable. The only relationship that was statistically significant was a greater improvement in mobility with increased total fat mass and IMAT loss.
The above data suggests that individuals with more total and intermuscular adiposity are at a physiologic disadvantage with respect to muscular adaptations in response to resistance training. Previous research has suggested this may be related to reduced adaptation to increased loading, reduced mitochondrial function and capillary density, or interference with contractile proteins perhaps secondary to local release and elevated concentrations of fatty acids or cytokines by fat.
To diet or not to diet?
This study clearly shows that resistance training alone in an older overweight-obese population improves body composition, including a reduction of IMAT, as well as muscle strength, power, and quality and overall physical performance. The addition of a caloric deficit further improved body composition while maintaining all muscle-function improvements seen in the RT only group, and led to improved mobility and reduced self-reported disability. Importantly, both protocols were safe and well tolerated as evidenced by the very high overall compliance of the subjects and lack of adverse events.
It is unfortunate that the diets were not reported, as the loss of LBM in the RT+CR group may very well have been owed to a lower intake of protein, especially considering that the meal replacements given for breakfast and lunch were Slim-Fast shakes and bars that contained ~220 kcal with 7–10 g protein, 33–46 g carbohydrates, 1.5–5 g fat, and 2–5 g fiber. We did see earlier this week, after all, that at least 1.2 g/kg of protein is necessary for the prevention of muscle loss while dieting in older obese adults.
Nonetheless, it does indeed appear prudent to lose weight while engaging in resistance training for the most benefit in obese older folk.