Het tegengaan van sarcopenie en functionele achteruitgang door middel van krachttraining

The aging of population poses many challenges to our society. A major public health concern is the age-related decline in functionality, which threatens the independency and quality of life of older adults. This functional decline has been shown to be associated with the phenomenonof sarcopenia, first introduced by dr. I.H. Rosenberg as the age-related decrease in skeletal muscle mass.As our understanding of the complex process of aging progresses, proposed definitions of sarcopenia go beyond a decrease in muscle mass, including a reduction in muscle strength, in muscle power (the ability to generate force quickly), and in functional performance. Maintenance or even gain in muscle mass at age does not necessarily prevent muscle weakness. Previous findings imply thatmuscle power and the ability to develop a high velocity during muscle contraction are strong predictors of everyday function of older adults, whereas muscle mass seems less decisive for activities of daily living. Thus, for the detection of preclinical functional limitations, attention should also be paid to force-velocity characteristics of skeletal muscle. However, there is a paucity of research regarding the relationship between these force-velocity characteristics, muscle mass and functional limitations in older adults.Resistance training is widely recognized as an important countermeasure against muscle atrophy, muscle weakness and functional decline. In order to maximize gains in muscle strength and mass, international guidelines currently recommend training at high external resistances (70-85% of one repetition maximum (1RM)). However, the use of such high resistances may sometimes be contraindicated in older adults, suggesting that low-resistance exercise protocols might be more suitable. To date, research remains inconclusive on whether low-resistance exercise is as effective as high-resistance exercise in inducing hypertrophy and strength gains in older adults. There is some evidence that achieving maximal effort in training protocols may be necessary to maximize training-induced gains.This doctoral thesis consists of two chapters. In chapter 1, we focus on gaining a better insight in the relationship between force-velocity characteristics, muscle mass and functional performance in elderly persons. Chapter 2 investigates the feasibility and the effects of strength training at different external resistances on muscle performance and functional capacity. In chapter 1, discussed in paper 1 of this doctoral thesis, the main objective was to determine the relative contribution of muscle strength, force-velocity characteristics and muscle mass to functional performance. Subjects were 123 elderly women (aged 79.67 ± 5.25 years). The results emphasize the role of muscle strength and speed of movement of the knee extensors in everyday function of elderly women. Muscle mass, however, was not an independent determinant of functional performance when included in the same regression model as muscle strength, suggesting that muscle mass primarily contributes to functional performance through its association with muscle strength. This highlights the importance to focus on several aspectsof muscle function in addition to muscle mass, not only when identifying persons at risk for functional limitations but also when designing exercise interventions to prevent functional decline.Chapter 2 of this doctoral thesis consists of two subchapters. Subchapter 2.1 (paper 2) explored the feasibility of an experimental high-repetition low-resistance exercise protocol in young adults, so that it could be fine-tuned before applying it to older adults. Paper 2 additionally investigated the impact of external resistance and maximal effort in strength training programs on muscle strength and force-velocity characteristics in young adults (N = 36). Two low-resistance exercise protocols were created and compared to high-resistance exercise (HImax) over a 9-week training period: one low-resistance protocol ending in maximal effort (LOmax), one low-resistance protocol without achieving maximal effort (LO). All training groups performed one set of 10 to 12 repetitions, but training intensity differed between groups. HImax trained at a resistance of 80% of 1RM ending in maximal effort; LO trained at a resistance of 40% of 1RM without achieving maximal effort; LOmax trained at a resistance of 40% of1RM (similar to LO), preceded by a fatiguing protocol of 60 repetitionsat 20% of 1RM. No rest was provided between sets, which led to maximal effort in LOmax. The findings in paper 2 suggest that training until maximal effort, probably resulting in optimal activation of the muscle, is needed to optimize strength gains in low-resistance exercise protocols. Interestingly and unexpectedly, the experimental high-repetition low-resistance exercise protocol (LOmax) showed promising and advantageous results on dynamic strength and speed of movement.Subchapter 2.2 (papers 3 and 4) aimed at comparing the effects of high- and low-resistance exercise on muscular and functional outcomes in older adults (N =56). In paper 2, LOmax appeared to be effective in inducing strength gains in young adults, but it remained to be elucidated whether this exercise protocol was also effective in older adults. In addition, the resistance exercise protocols in paper 2 did not allow for conclusions on whether or not the increase in resistance at the end of a single low-resistance exercise set (see LOmax) is crucial for optimal effects. Therefore, two low-resistance exercise protocols were created and compared to high-resistance exercise (HIGH) in papers 3 and 4: one high-repetition low-resistance protocol (LOW) in which external resistance is kept constant within one session, one mixed high-repetition low-resistance protocol (LOW+) in which resistance was increased after 60 repetitions (similar to LOmax in paper 2). All protocols were designed to end in maximal effort. Paper 3 focused on the immediate post-intervention effects after 12 weeksof training, whereas paper 4 evaluated the residual adaptations 24 weeks after the end of the intervention. Paper 4 additionally investigated the long-term exercise adherence of participants in HIGH, LOW and LOW+. The results of subchapter 2.2 suggest that high- and low-resistance exercise protocols until muscle failure are equally able to counteract the age-related declines in muscle mass, basic muscle strength (isometric and isokinetic strength at low speed) and functional performance. Our data also suggest the importance of long-term maintenance of resistance exercise behavior for increasing or maintaining muscle mass and muscle function, but indicate that various aspects of muscle strength and functional performance remain elevated for several months after the end of a supervised training intervention. When compared at follow-up, low-resistance exercise until muscle failure appears to be as effective as high-resistance exercise for maintaining training-induced neuromuscular and functionaladaptations. These findings point out that it is time to re-think or atleast nuance the high-resistance training philosophy that has gone unchallenged for decades. Low-resistance exercise is valuable in older age as alternative to high-resistance exercise. However, long-term maintenance of resistance exercise behavior remains a challenge among older adults.status: publishe