Three main findings of this study were that (a) the time course for improvements in upper and lower body muscle strength, functional mobility and submaximal endurance capacity over 16 weeks was different; (b) gains in muscle strength and submaximal endurance capacity were not completely lost after 16 weeks of detraining (DET) and (c) leg muscle strength is an important correlate to submaximal endurance capacity in older individuals.
It was found that both arm and leg muscle strength improved significantly (39 ± 27 % and 167 ± 125 %, respectively) over the course of 16 weeks in older individuals who had no previous experience in resistance training (RT). The observed changes were already significant after 4 weeks; thereafter more gains were achieved every 4 weeks until the completion of the programme. The increase in the participants’ leg strength was significant after each month of training, suggesting that the progression in training loads for the leg exercises were well structured for the participants. Furthermore, seeing a steady monthly improvement in muscle strength will very likely be a strong motivating factor for older adults. The results support previous findings that noteworthy muscle strength increases can be achieved within 12 sessions in ageing individuals [15, 20], irrespective of training frequency per week. Pinto et al.  reported an improvement in the leg strength of elderly women after completing 12 lower body strength training sessions, while Lovell et al.  observed a similar improvement in older men. The latter study also reported a significant improvement in leg strength after each month of training over a 16-week training period. The present study adds to the existing literature by showing that 12 RT sessions result in a marked increase in upper body muscle strength and that after 48 sessions there was still no indication of a plateau in the improvements of both upper and lower body strength.
Modest, but statistically significant improvements in functional mobility [Timed-Up-and-Go (TUG) test] and submaximal endurance capacity during the Bruce test were observed only after 16 weeks of RT (3 ± 10 % vs 19 ± 29 %, respectively). These results are in contrast with previous findings where significant changes in physical function were evident after a shorter time period. Pinto et al.  found significant increases in physical function and muscle strength after 6 weeks of lower body strength training in elderly women, while others reported improved physical function after 12 weeks RT [9, 10]. The fact that a significant improvement in functional mobility in the current study was only observed at the end of the intervention may possibly be attributed to the fact that the RT programme did not focus exclusively on the leg muscles, but also included arm exercises. Furthermore, studies also vary in terms of training intensities, with this study employing higher exercise intensities than most others. In a meta-analysis Steib et al.  concluded that although higher training intensities (> 60 % 1RM) lead to greater gains in muscle strength, it is not necessarily more advantageous for improvements in physical function in older adults compared to low and moderate intensity RT. It should also be noted that only Pinto et al.  included a control group in their studies. Without a control group one cannot be certain that enhanced performances can be attributed to the training programme alone, as one cannot exclude the possibility of the Hawthorne effect, the learning effect, or normal day-to-day variation as reasons for the findings.
The participants’ improvement in submaximal endurance capacity in response to RT is in agreement with previous reports. An increased submaximal endurance capacity after RT could be the result of peripheral adaptations in the trained muscles, which have been reported in other RT studies. Lovell et al.  found an increase in arterial-venous oxygen difference after 16 weeks of strength training, while cardiac output remained unchanged. Researchers suggested that this increased ability of the muscles to utilize oxygen is the result of increases in capillary density and mitochondria in the trained muscles [15, 22]. It has also been proposed that resistance training results in the recruitment of less motor units by the working muscle, consequently prolonging the onset of total muscle fiber fatigue [14, 22].
Even though there was a decrease in the participants’ muscle strength at follow-up, their level of strength was still significantly higher than the values obtained at the pre-test. This finding is also in line with previous research. Despite a significant decrease in muscle strength after 20 weeks of DET following an 18-week progressive RT intervention, Harris et al.  reported that their participants’ muscle strength was still significantly higher compared to baseline values. The same trend was described by Geirsdottir et al. , where participants completed DET tests over a period of 6 to 18 months following a 12-week RT programme. These findings reflect the long lasting effects of well-designed progressive RT programmes and suggest that even if individuals cannot train for a period of time, all is not lost.
Functional mobility returned to pre-training values after 16 weeks of DET, despite the significant retention of leg strength. This finding is in agreement with the results of Correa et al. , but in contrast to the findings of Geirsdottir et al. . Both studies investigated the effects of 12 weeks of RT, which was followed by DET periods of 12 months and longer. The inconsistencies in these findings could be a function of the differences in the frequency, duration and intensity of the interventions, as well as the follow-up periods. Furthermore, it should be noted that different functional mobility tests are used in the various studies and it is questionable whether the outcomes for these different tests (i.e., TUG, 30s sit-to-stand, stair climbing etc.) are comparable.
Table 2 shows that there were significant improvements in submaximal endurance capacity in both groups after the follow-up period. However, upon closer inspection of the data it was evident that only two participants in each group showed a pronounced improvement from post-test to DET [19.5 and 28 % in RT group and 67.2 and 24.8 % in control (CON) group], consequently affecting the group’s overall results. When these outliers are omitted from the data set, it shows that both groups did indeed perform better after DET, however, the improvements in performance were not statistically significant.
Our findings suggest that enhanced leg muscle strength is a better determinant of submaximal endurance capacity, than of functional mobility as assessed by the TUG test. This is probably because performance in the TUG test is more dependent on coordination, balance and reaction time, which are not necessarily enhanced by RT.
This is the first study to show that gains in functional mobility and muscle strength do not happen simultaneously. Whereas upper and lower body strength was significantly enhanced after 4 weeks, the improvement in functional mobility was only evident after 16 weeks. Longer term intervention studies (> 4 weeks) only reported pre- and post-training results and therefore it is unclear if this finding is unusual. It is not clear if this pattern is a function of our specific training programme, whether it is due to differences in the time course of physiological adaptations (i.e., peripheral and central adaptations), whether it is a finding limited to our population (i.e., low strength levels, but higher levels of functional mobility at the beginning of the study), or if it is a function of the sensitivity of the selected physical tests to change. According to the relative norms for upper and lower limb strength , the participants’ overall muscle strength was below average for men and women in both the 50–59 and greater than 60 years age categories prior to the intervention, while their TUG results were above average . Therefore, the participants in this study had greater capacity to improve their muscular function than their functional mobility. Future studies should determine if participants with lower levels of functional mobility show similar patterns of change over the course of a physical intervention programme compared to the current study.