In the present study, an increase in HRQOL accompanied by an increase in total muscle mass and muscle strength, was seen in older adults following 12 weeks of strength training. Further, the improvement in strength was related to better physical and social function, and to a perception of better general health, although the association can be considered as modest. According to the increase in HRQOL, it is notable that, despite their baseline scores being above national norms [26], two of the eight HRQOL SF-12 scores, role physical and general health, increased, as did physical component summary scores. The SF-12 role physical domain addresses physical health-related role limitations, including limitations regarding type of work or other usual activities, and fewer accomplishments than the respondent would have liked. The general health scale reflects the respondents’ consideration of their own health [23]. Our results showed an increase in these domains after the intervention, indicating that systematic training may be positive for the participants. Strength training may contribute to a feeling that one has fewer physical limitations and can more easily carry out everyday activities such as walking long distances, climbing stairs, and balancing [27]. This may be positive for the perception of own health status. Better physical health is essential for individual autonomy, and improved muscle strength may contribute to better function and greater activity [14].
Strength training may improve not only muscle strength and mobility, but also physical and social capabilities, including older adults’ capability of performing both simple and more complex daily activities [1]. General muscular weakness is associated with aging, and even small improvements in strength and mobility can be considered important [28]. Our findings also support the notion that promoting systematic strength training in older men may have an impact beyond functional capacity, as it was associated with a positive perception of one’s own health. Another explanation for the improvement in HRQOL may be the positive social aspects of being part of a group, which may have positive psychological and physiological effects [7].
The benefits of PA on health are well known from earlier studies, but the relationship between type of PA and HRQOL have not been well described. Our findings are in accordance with Pihl et al. [19], who demonstrated that HRQOL significantly improved in older adults (mean age, 76.2 years) who were part of a strength training intervention group as measured using the SF-36; general health and the physical component scores were significantly improved at 3 months compared with the control group [19]. A study among older American adults (>65 years) showed that progressive resistance and balance training were associated with enhanced HRQOL [13], and a study among older Finnish adults demonstrated positive effects of combined strength and endurance training on some dimensions of HRQOL measured with SF-36 [5]. However, unlike our study, these studies included both older men and women.
In contrast to our findings, the results of a recent Norwegian intervention study showed no effect on self-rated health on the physical or mental subdomains of the SF-12 after 3 months of strength training in older adults recovering from hip fracture [29]. However, our study was conducted in a healthy population of older men, and one must bear this in mind when comparing these findings.
One previous study explored the relationship between different types of group exercise and HRQOL, and concluded that intense exercise and strength training had the greatest effect on HRQOL [7]. In contrast to our study, however, this latter mentioned study included both middle-aged women and men.
Findings from our study also showed a significant increase in total muscle mass and muscle strength in the arms, legs, and trunk after the 12-week strength training program. Strength training is considered important to prevent general muscular weakness, which is associated with aging [28]. The importance of strength training for older adults is also underlined in the guidelines, which recommends older adults to perform exercises that increase large muscle group strength 2 or more days a week [9].
Weak to moderate positive correlations were found between changes in leg extension and physical function, and also between arm and social function in our study. This shows that improvements in strength may be important in relation to HRQOL, especially the physical and social function. A study by Gary et al. [30] also demonstrated that better leg muscle strength was related to better physical function and increased HRQOL in older adults. However, we have no explanations for the negative correlations between leg extension and social function, and for biceps curl and general health.
Strengths and limitations
The main strengths of the present study were the high attendance rate, the frequent meetings with highly qualified instructors, and the close follow-up. We included 2 weeks with familiarization to the strength training, and all measurements were performed by the same test leader and in the same order each time. However, some potential limitations have to be considered when interpreting the results of this study. Due to the lack of a control group, the possibility that other factors in addition to the strength training contributed to the improved HRQOOL and strength cannot be ruled out. The intervention duration was relatively short, and the sample size was small, which may have contributed to type II errors. Moreover, our results showed that baseline SF-12 scores were significantly higher than SF-36 scores for the general population in this age group [26], indicating that our sample included relatively healthy older men who may not be representative of the older Norwegian adult population. Only men were included in the study, and the results might have been different if also women were included.