A few weeks ago I wrote about what I called The Resistance Training Paradox, the paradox consisting of the fact that resistance training (weightlifting) promotes growth, and a necessary trade-off exists between growth and longevity. Exercise, however, is health- and longevity promoting. So how could resistance training both promote growth and aging and be a health-promoting exercise? One or the other must give. This post is about resolving the resistance training paradox.
I believe the answer is that resistance training does not in fact promote aging, and is health- and longevity-promoting. The explanation follows.
The hormone that is mainly responsible for growth, including growth of muscle tissue, is insulin-like growth factor 1, or IGF-1. Growth hormone itself (GH) appears to act by increasing the amount of IGF-1 in circulation.
IGF-1 definitely promotes aging. For example, humans who are genetically deficient in growth hormone receptors have “severe GHR and IGF-1 (insulin-like growth factor–1) deficiencies”, and the title of the article from which this quote comes is instructive: Growth Hormone Receptor Deficiency Is Associated with a Major Reduction in Pro-Aging Signaling, Cancer, and Diabetes in Humans. In mice, genetic deficiency of IGF-1 means longer life. A recent review by two stalwarts in anti-aging research, The key role of growth hormone–insulin–IGF-1 signaling in aging and cancer, states, “The life-prolonging effects of caloric restriction are likely related to decreasing IGF-1 levels.” And by the way, there are many, many studies linking IGF-1 to aging and its diseases; no cherry-picking of studies here, I’m not making this up.
So, calorie restriction, a known life-extender, appears to work by decreasing IGF-1 levels. IGF-1 in turn modulates autophagy, i.e. the more IGF-1, the less autophagic activity. We saw in a recent post here that autophagy is critical for the optimal anti-aging strategy.
IGF-1 promotes growth. So does resistance training. However, resistance training does not result in higher IGF-1 levels. In Hormonal Responses and Adaptations to Resistance Exercise and Training, the authors, again experts in this field, state that the IGF-1 response to resistance training is an acute one, and that resting concentrations remain normal. Another paper, Resistance training alters plasma myostatin but not IGF-1 in healthy men, reported on a study of volunteers who underwent 10 weeks of resistance training, and reported that “IGF-1 did not change from pre- to post-training”. Myostatin, however, did decrease substantially, which presumably accounts for muscle growth. Conclusion:
Myostatin may play a role in exercise-induced increases in muscle size, its circulating levels decreasing with resistance training in healthy men. Exercise of the whole body versus the elbow flexors alone did not provide a supplementary stimulus in altering resting plasma IGF-1 or myostatin, or in increasing muscle strength or size. Thus, by default, growth factor responses local to the muscle may be more important than circulating factors in contributing to muscle hypertrophy with resistance training.
Resistance training does not increase circulating levels of IGF-1, except perhaps acutely, within an hour or two after the workout. Therefore resistance training does not promote aging.
But, we’re still left with the growth-longevity trade-off, and there is something peripheral to resistance training that does appear to promote aging, and that is high protein. I’ll have more to say about this in a future post.
The insulin/IGF-1 signaling in mammals and its relevance to human longevity
‘Anti-Aging’ Hormone May Actually Shorten Life
The paradox of the insulin/IGF-1 signaling pathway in longevity.
Protein and amino acid restriction, aging and disease: from yeast to humans
Long-term effects of calorie or protein restriction on serum IGF-1 and IGFBP-3 concentration in humans
Chronic resistance training activates autophagy and reduces apoptosis of muscle cells by modulating IGF-1 and its receptors, Akt/mTOR and Akt/FOXO3a signaling in aged rats
GDF11/Myostatin and aging. This article actually may make a case against resistance training.
Prolonged Fasting Reduces IGF-1/PKA to Promote Hematopoietic-Stem-Cell-Based Regeneration and Reverse Immunosuppression