In a recent short interim report published in the journal BMJ Open Sport & Exercise Medicine, researchers investigated the long-term effects of varying intensities of supervised resistance training in retirement-age adults.

Study findings highlight that high resistance training (HRT) cohort participants maintained muscle performance, particularly in their isometric leg strength. In contrast, the muscles of participants in the moderate-intensity training group (MIT) and the non-exercise control group (CON) were observed to decrease in strength (and, by extension, functionality) significantly over the three years following the termination of the supervised training baseline study.

Background

Modern medical progress has substantially prolonged the global human lifespan. An unintended outcome of this otherwise positive advancement is the surge in age-associated chronic health conditions (e.g., cardiovascular diseases [CVD] and cancers) and a loss of autonomy in aging individuals.

Recent research has suggested that, while the normal aging process contributes to skeletal muscle reductions and, in turn, autonomy losses, resistance training may help maintain muscle strength, thereby attenuating suboptimal outcomes. Unfortunately, most studies on the topic are short-term, with a significant absence of data on the long-term benefits of supervised muscle training on individuals above retirement age.

The Live Active Successful Aging (LISA) study was a large cohort, a randomized controlled trial carried out in 2020 on 451 participants over retirement age (~64-75 years; mean age at study initiation was 67). The study age, sex, body mass index (BMI), and chair-rise test performance (a test of leg strength and endurance) matched participants into three cohorts – high resistance training (HRT; n = 149), moderate-intensity training (MIT; n = 154), and non-exercise controls (CON; n = 148) to elucidate the long-term outcomes of resistance training across differing intensities.

Interventions in the training cohorts were supervised and machine-based, comprising three full body sessions per week over one year. The Brzycki prediction equation was used to determine the intensity of training in HRT (3 sets of 6–12 repetitions at ~70%–85% of 1 repetition maximum [RM]) and MIT (3 sets of 10–18 repetitions at ~50%–60% of 1 RM).

Initial study findings and those at the first round of long-term follow-up (one year) revealed that while the HRT cohort maintained skeletal muscle strength and function, these variables were significantly reduced in MIT and CON cohort participants. This suggested that exercise alone may be insufficient in maintaining optimal muscle function. Exercise intensity may be essential in achieving desired outcomes.

About the study

The present interim report is a part of the long-term follow-up with LISA participants and is conducted four years after the initial study. Additional reports are intended in three and six years following this one.

The present study comprised 369 out of the original 451, with the remaining 82 adults dropping out due to lack of motivation or severe ongoing illness. The study cohort has a mean age of 71 and is 61% female. Study data collection was carried out over three days. It included a complete health screening (Day 1), dual-energy X-ray absorptiometry (DXA), visceral fat mass estimation, isometric leg strength evaluation (Day 2), and brain and thigh magnetic resonance imaging (MRI) scans (Day 3).

Additionally, daily step count was measured using an accelerometer as a proxy for daily physical activity across participants. Statistical analyses between cohorts were carried out using the Student's paired t-tests (to estimate changes from baseline) and two-way mixed model analyses of variance (ANOVAs) to elucidate between-group differences. Models were controlled for sex and age, and Bonferroni corrections were applied to multiple comparisons.

Study findings

Study dropouts, particularly those who withdrew due to lack of motivation, were observed to have higher mean body weight, BMI, and waist circumference at baseline than participants who persisted through year four of follow-up. Notably, the outcomes of resistance strength training in participants and dropouts (measured at the previous one-year follow-up) did not differ statistically.

Encouragingly, daily physical activity evaluations of study participants revealed that, despite progressing age (mean = 71), participants were still active, on average almost meeting the 10,000 step optima recommended by scientists and clinicians for individuals half their age. Baseline-to-present comparisons revealed that while significant reductions in isometric leg strength were observed in MIT and CON cohorts, strength was maintained at approximately baseline values in HRT participants, signifying no losses in functionality despite four years of additional aging.

Overall muscle strength was observed to follow similar trends – while MIT and CON cohorts presented substantial losses compared to baseline readings, the HRT cohort gained muscle strength compared to baseline (pre-intervention) values. Notably, all three cohorts were observed to have undergone reductions in lean leg mass.

These results imply that the HRT cohort gained muscle functionality despite losing muscles. Additional research is required to elucidate the mechanisms (neural or physical) underpinning these findings.

Lean body mass and visceral fat estimations were observed to be most optimal in HRT participants (reductions), while MIT (no change) and CONS (significant increases) individuals presented suboptimal group*time outcomes over the four-year gap since baseline evaluations. Handgrip strength and leg extensor power, the currently accepted metrics of muscle functionality, displayed time-associated reductions across all cohorts.

Surprisingly, while the between-cohort functionality differences were statistically significant (HRT > MIT > CONS), within-group deltas (Δchange) did not change across the four-year follow-up. The authors hypothesize that this may be due to the dataset comprising participants who are substantially more active than average 71-year-olds, though additional research is required to elucidate this observation.

Conclusion

In summary, these findings highlight the role of training intensity in long-term muscle strength and functionality maintenance. These findings come with caveats – while the HRT group depicted significantly improved leg-strength maintenance compared to MIT and CON cohorts, handgrip strength, the currently accepted measure of overall muscle strength, was indistinguishable between cohorts.

"Notably, benefits in leg strength were present despite lowered leg lean mass. Neural adaptations influence the response to resistance training. The present results suggest that these adaptations might play a role even as lean leg mass and thigh CSA decrease."

These findings highlight that one year of high-intensity resistance training can have prolonged muscle strength and functionality benefits in aging adults for four years or more, while lower-intensity training programs do not share these benefits.