We found that the 12-week, low-intensity, resistance exercise training program improved metabolic factors, such as blood pressure, lipids (e.g., total cholesterol and triglyceride) and insulin, muscle hypertrophy, and inflammatory markers in aged sedentary women. These results suggest that even low-intensity exercise is beneficial for aged sedentary women. Furthermore, the inverse correlation between percentage changes in subscapular muscle thickness and percentage changes in CRP and TNF-α suggests that exercise training-induced muscle hypertrophy is associated with reduced levels of inflammatory markers and cytokines; this finding supports the hypothesis that low-intensity exercise training is effective in reducing chronic inflammation in elderly, sedentary women.
Inflammation may be associated with the age-related loss of muscle mass and strength [28
]. Loss of skeletal muscle is the major factor that contributes to frailty and has a profound impact on the quality of life of older people [28
inhibits myogenic differentiation [29
] and promotes protein catabolism [29
]. In addition, TNF-α
reduces skeletal muscle protein synthesis by decreasing translation initiation [30
]. In the present study, the training program induced increased muscle thickness in the upper arm, abdomen, and subscapularis. In particular, the absolute percent change in subscapular muscle thickness (as compared to the other muscles) was associated with a reduction in inflammatory markers. Ultimately, these findings may reflect the focus on arm-specific exercises within this intervention program.
The circulating levels of CRP, SAA, and HSP70 decreased in elderly women in response to the present exercise training program (). SAA is produced by hepatocytes and secreted into the serum as well as CRP [31
]. Both SAA and CRP show a strong independent relationship with future cardiovascular events [6
]. Although the physiological significance of SAA remains controversial, some studies have demonstrated that SAA associates with HDL-cholesterol to remove it from the site of inflammation [31
]. In the present study, the levels of HDL-cholesterol did not change after the exercise training program, and we did not find a correlation between HDL-cholesterol and SAA or CRP. This discrepancy may be due to the smaller sample size of the present study. Therefore, larger more diverse studies assessing changes in HDL-cholesterol and its relationship with CRP and SAA following exercise training are warranted.
In previous studies, serum HSP70 concentrations were found to be elevated in patients with hypertension [34
], peripheral and renal vascular disease [35
], cerebral ischemia [36
], intermittent claudication [37
], and critical lower limb ischemia [37
]. The serum HSP70 concentration decreased following a 14-week cardiac rehabilitation therapy, statin treatment, and a combination therapy of rehabilitation and statin for patients with coronary artery disease [38
]. Therefore, we interpret the reduction of HSP70 in our study as an indication that exercise training reduces inflammation. The mechanism by which circulating levels of HSP70 (e.g., extracellular HSP70) are involved in systemic low-grade inflammation is not known. While HSPs are leaked into the extracellular compartment due to necrotic cell death [39
], HSP70 can be released independently of necrotic cell death in response to a number of stressful conditions including exhaustive exercise [40
]. Future investigations will explore the physiological significance of extracellular HSPs.
Growth factors such as insulin-like growth factors (IGFs) are related to insulin and mediate many actions of growth hormone, including promotion of myoblast proliferation, differentiation, and protein accumulation in muscle. Serum IGF-I levels decrease with age and are regarded as a potential mediator of sarcopenia [41
]. Therefore, IGF-I levels may reflect distal outcomes of clinical importance in the elderly, such as objective performance on muscle-dependent tasks and mobility in the elderly. However, in the present study, the level of plasma IGF-I decreased after the exercise program. The results from prospective training studies are controversial, as the levels of IGF-I in different studies have been elevated [42
] or reduced [43
] following a strenuous training program for 4–11 weeks in young individuals. Future investigations will explore the physiological significance and interpretation of the exercise training—induced reduction on circulating levels of IGF-I.
The limitations of the present study were the lack of control group, small sample size, and no records for the daily physical activity outside of the sessions. Considering that the average number of sessions (14.4 ± 3.7) was more than 12, the results may be due to the motivation of the participants to exercise. The participants were encouraged to increase their physical activity during the intervention period. The number of daily steps was recorded for some of the participants (n = 10). There was an increase in the average number of daily footsteps from the 1st week (2100 steps per day) to the 12th week (3000 steps per day). Also, the participants enjoyed their interactions with the young instructors and college students who visited and talked with them every week during the exercise sessions. Thus, there might be a physiological confounding factor in the increase in daily activities that contributed to the reduction of these metabolic factors. In addition, none of the results were significant after applying a Bonferroni correction. It is possible that there were spurious positive tests due to the large number of statistical comparisons performed.