Human aging is associated with a loss of muscle mass, a deficit in muscular strength and impairment in performing some activities of daily life. Typically, these changes start to occur about age 40 and progressively worsen with aging.
Sarcopenia can be defined as natural, age-related loss of muscle mass, strength and muscle function. It is estimated that 7% of adults over 70 and 20% over 80 are affected by very debilitating sarcopenia, costing the U.S. healthcare system more than $18 billion a year (Melov et al. 2007). The causes of this muscle aging are multifactorial, with theories and research suggesting it is related to oxidative stress (a condition in which antioxidant levels are lower than normal), cell death, inflammation (an immune response to injury or infection), hormonal dysregulation, inactivity, alternations in protein turnover, and dysfunction of the mitochondria (the ATP energy factory in cells) (Melov et al. 2007).
Resistance training with older populations has been shown to reduce markers of oxidative stress and increase antioxidant enzyme activity. Melov and colleagues (2007) investigated whether resistance training actually affects some of the gene expressions associated with muscle aging, thus reversing the aging process. (See the sidebar “Relevant Genetic Terms” for a glossary of genetic terms.)
Older and younger people were chosen for this study. All were nonsmokers. The 25 older volunteers (mean age = 68 years) self-reported doing walking, gardening, tennis or cycling three or more times per week. The 26 younger subjects (mean age = 24 years) were relatively inactive, self-reporting only modest recreational activity. The researchers deliberately chose a relatively active older population and a relatively sedentary younger population because they felt it would help them look at the effects of aging, rather than simple inactivity, if both groups were fairly well matched in terms of how active they were. All subjects went through a medical evaluation, a health history assessment, a resting electrocardiogram (for detection of any irregular heart rhythms) and a submaximal graded exercise test on a cycle ergometer before being admitted into the study. Subjects were excluded if they showed any orthopedic limitations to exercise or evidence of heart disease or kidney problems.
Training and Testing
All subjects performed supervised resistance exercise on two nonconsecutive days of the week (Monday/Thursday or Tuesday/Friday) for the 26 weeks of the study. Subjects performed 12 different exercises: chest press, leg press, leg extension, leg flexion, shoulder press, lat pull-down, seated row, calf raise, abdominal crunch, back extension, biceps curl and triceps extension. Subjects began with single-set training at 50% of their one-repetition maximum (1RM) and gradually increased to 3 sets at 80% of their 1RM during the course of the study. Participants retested their 1RM for all exercises every 2 weeks, and the training loads were adjusted accordingly to 80% of their 1RM. Subjects were also tested for peak maximal isometric (muscle action where there is no limb movement or change in joint angle) knee extension strength of the right leg at the beginning and end of the study.
Muscle Biopsy Testing
Each of the younger subjects had a muscle biopsy (incision and extraction of a small piece of muscle) taken from the vastus lateralis muscle before and after the 26-week study. Each of the older subjects also underwent a pretest biopsy, and 14 of them had post-training muscle biopsies. RNA was extracted from the muscle for analysis to determine the genes that were expressed differentially (unusually) with age (meaning they were atypical to other genes being analyzed).
The researchers identified 596 differentially expressed genes. Of these, after 26 weeks of resistance training, the researchers identified 179 age- and exercise-associated genes showing a reversal of their gene expression. This means quite literally that the resistance training was not only slowing but also reversing the aging process at the gene level. The gene expressions of the resistance-trained older subjects demonstrated characteristics similar to those of the younger group. The researchers also noted that mitochondrial impairment, normally seen with inactivity, was reversing in response to the 6 months of resistance training.
With regard to muscular strength, the peak isometric strength of the older population was initially 59% lower than that of the younger population. By the end of the training, the older group’s peak strength was only 38% less than that of the younger group, representing a significant improvement for the older population.
This novel study demonstrates that resistance training can reverse aspects of aging at the gene level. For years, personal trainers and fitness professionals have touted the functional movement and health benefits of resistance exercise. Now trainers can share with their clients that regular, progressive resistance training (see the sidebar “Mature Clients: Top 10 Training Tips”) also improves the muscle’s longevity profile at the molecular level. It is well-known that long-term resistance training is associated with a lower risk of age-associated morbidity and mortality. This original study may be a first step in explaining how some of these positive changes occur. n
Sidebar: Relevant Genetic Terms
The following is a brief glossary of selected genetic terms.
DNA (deoxyribonucleic acid): a group of complex compounds found in all living cells that carries the genetic information in the cell and is capable of self-replication and the synthesis of RNA
gene: a small piece of DNA that instructs the body how to build a specific protein; there are approxi┬¡mately 30,000 genes in each cell of the human body
gene expression: the conversion of the information encoded in a gene first into messenger RNA and then into a protein
messenger RNA: the form of RNA that mediates the transfer of genetic information from the cell nucleus to ribosomes in the cytoplasm, where it serves as a template for protein synthesis
RNA (ribonucleic acid): a chemical found in the nucleus and cytoplasm of cells that plays an important role in protein synthesis