The aging athlete: endurance or strength for younger muscles?

Exercise type and muscle aging

The evidence that vigorous exercise helps slow the aging process and adds healthy years to the human lifespan is incontrovertible. But which type(s) of intense exercise could deliver the best results? To date, most of the research has focused on endurance training, with a particular interest in the role of interval training. Interval training delivers intensity in a more manageable way, and can be adapted to suit everybody – from beginners to elite athletes (for a more in-depth discussion, see this article). This focus is understandable; heart disease is the biggest preventable cause of early death, so exercise strategies that improve cardiovascular health were obvious candidates for research.

One aspect of this topic that is relatively poorly understood however is the link between exercise and muscle health and aging. If you think about it, this is actually quite an important consideration. That’s because the exercise can only take place via the movement of muscles. If certain types of exercise can help keep muscle cells and fibers healthy and ‘young’, the capacity of muscles to engage in vigorous exercise as the years tick (ie well into older age) can be better sustained. Biologically younger and healthier muscle tissue means that vigorous exercise can be performed later in life, which creates a kind of virtuous circle: exercise that keeps muscle cells and fibers young enables vigorous exercise to continue, thus slowing down biological aging and keeping muscle tissue young!

While endurance training involves rhythmic and regular contractions of large muscle groups, the intensity on those muscles is necessarily low (if it weren’t, the muscles would quickly fatigue and the endurance training would have to cease). Therefore, when it comes to intensely training muscles rather than the cardiovascular system, strength training reigns supreme. When muscles are strength trained, the acute intensity stimulates a wide array of adaptation mechanisms in the muscle; indeed, research shows that as many as 1,290 genes involved in muscle growth, renewal and adaptation are upregulated (ie become more active) in individuals who resistance training regularly⁽⁸⁾. This being the case, some scientists have wondered whether resistance training could actually be superior to endurance training for keeping muscles young.

New research on exercise type

To try and answer this question a team of Danish and Norwegian scientists have carried out some fascinating research⁽⁹⁾. Published in the Journal of Applied Physiology, this study sought to investigate and compare the impact of life-long strength versus endurance training on muscle fiber type and fiber quality in older athletes. The researchers also compared the muscles fibers of these older athletes to those of young, healthy and active adults.

The researchers noted that the key hallmarks of muscle aging involve decreased muscle strength and a decrease rate of force development (ie loss of speed and power). These losses are partly explained by muscle motor unit dysfunction caused by a process known as ‘denervation’ – ie where the motor neurons become damaged and develop lesions, which reduces their effectivenessto ‘fire’ muscle fibers with the appropriate electrical signals. This process leads to a subsequent loss of fast-twitch type II muscles fibers, which are the fibers used for powerful and quick muscle contractions. Therefore, they looked very closely at these attributes.

What they did

In this study, four groups of participants were investigated for markers of skeletal muscle denervation and reinnervation (where new neurons develop to replace damaged neurons), along with the proportion and quality of fast-twitch type II muscle fibres, and the prevalence of atrophied (ie shrunken and wasted) muscle fibres myofibers (defined as fibers with a cross-sectional area of 1494µm² or less). The four groups were as follows:

·        Lifelong strength-trained masters athletes (over 70 years of age).

·        Lifelong endurance-trained masters athletes (over 70 years of age).

·        Recreationally active but not lifelong trained adults (over 70 years of age).

·        Young habitually active adults (under 30 years of age).

As well as a studying a range of muscle fiber (vastus lateralis – the outer quadriceps muscle of the frontal thigh) markers using biopsies from all four groups, the researchers also tested each participants maximal leg press strength and their maximal rate of force development (ie ability to accelerate and generate power).

What they found

The results showed a number of surprising findings. There were as follows:

·        The lifelong strength-trained masters had pretty much the same type II fiber distribution (52.0%) as the active under 30-year olds (51.1%). This compared with just 39.0% type II fibers in the lifelong endurance-trained masters and 35.0% in the recreationally active but not lifelong trained over 70-year olds.

·        The rate of force development (ability to generate power) was greatest in the lifelong strength-trained masters (3993 Newtons per second), who exceeded even the active under 30-year olds (3470 Newtons per second).

·        Maximal leg press strength levels were (perhaps unsurprisingly) highest in the lifelong strength-trained masters (170kg), and significantly higher than in the young, active under-30s (151kg).

·        The presence of atrophied muscle fibers in the lifelong strength-trained masters (0.2%) was almost as low as in the active under 30s (0.1%). In the lifelong endurance-trained masters however, the proportion of atrophied fibers was no less than 1.2% - even higher than in the recreationally active but not lifelong trained over 70-year olds (1.1%).

The researchers concluded that the even though they were at least 40-50 years older than the young subjects, the strength-trained master athletes were characterized by similar muscle quality – but that this was NOT the case for lifelong endurance-trained masters athletes. These results therefore suggest that regular strength training over months and years can preserve muscle quality with advancing age in older adult – most likely as a result of regular use of high-intensity force generation during workouts. By contrast, this does not seem to occur in those who only endurance train.

Practical implications

For most athletes, whatever the sport, the implications of these findings will not be impactful on a day-to-day basis. However, for older athletes who are motivated not just by maintaining performance but also maximizing health into older years, the results are very significant. The bottom line is that while endurance training brings many health benefits, when it comes to muscle function and keeping your muscles biologically young, endurance training is not enough. Instead, regular strength training is a must!

What this means in practice is that as the years advance, it become MORE important to perform high-intensity strength work – not less important. This doesn’t mean you need to ditch all your endurance training; rather that you should consider substituting a couple of sessions per week with some strength worth. And just to reassure strength novices: adding some strength work doesn’t require lots of long workouts where you train to exhaustion. A simple 30-minute program targeting the major muscle groups with 2-3 sets of 8-12 reps (where the resistance is adjusted to enable you to only just achieve those reps), repeated a couple of times per week will be ample.

Endurance athletes should definitely not consider this wasted time either; a large body of research shows that endurance athletes (of any age) who add strength training into an endurance program can expect not only more strength, power and less chance of injury, but improved endurance performance also. That’s because strength training muscles also improves their mechanical efficiency during sub-maximal (ie steady-state) endurance exercise, reducing oxygen demand. So not only will your muscles stay younger, you’ll get faster into the bargain – a real win-win situation!

References

1.       Ageing Res Rev. 2021 Sep:70:101411

2.       Lancet. 1980;2:1207-10.

3.       Lancet. 1973;1:333-9.

4.       JAMA. 1995;273:1179-84

5.       Prev Med. 2001;29:37-52

6.       JAMA. 2002;288:1994-2000

7.       JAMA. 1989;262:2395-2401

8.       Exp Physiol. 2019 May;104(5):625-629

9.       J Appl Physiol (1985). 2023 Oct 26. doi: 10.1152/japplphysiol.00208.2023. Online ahead of print