A research paper published in the Journal of Applied Physiology has found that regular, intermittent exercise encourages amino acids to form proteins in muscle.
Anabolic resistance
Previous research has found that a lack of activity accelerates the age-related muscle loss known as sarcopenia [1]. This has been found to be strongly influenced by anabolic resistance, a phenomenon in which muscles fail to acquire sufficient proteins with which to rebuild tissue [2]. Therefore, suppressing anabolic resistance is a sensible strategy for slowing or preventing the deterioration of muscle tissue, particularly in the context of aging [3].
Previous research has found that physical activity encourages muscle protein development for up to 24 hours in young men [4], and other research has found that breaking up long sedentary periods with physical activity provides benefits to glucose and insulin use [5]. This paper takes this line of inquiry a step further, conducting biopsies to determine what happens in muscle fiber over the course of a day.
Marked proteins show the effects
In this study, all participants ate the same, standardized diet that approximates Western eating habits: prepackaged meals consisting of 55% carbohydrate, 30% fat, and 15% protein. A tracer was included to measure how much of this newly consumed protein was entering the muscle tissue. Participants were divided into three groups: an entirely sedentary control group (SIT), a group that performed 15 bodyweight squats every half hour (SQUAT), and a group that went for two-minute walks every half hour (WALK). The researchers refer to these exercise breaks as ‘activity snacks’.
While exercise caused the tracer to simply vary more in blood plasma while the average among participants remained approximately the same, the effects on muscle protein synthesis were clear within muscle tissue. While there were outliers, the SQUAT and particularly the WALK group enjoyed significantly more muscular protein synthesis than the SIT group did.
Interestingly, the SQUAT group, not the WALK group, showed an increase in a marker related to mTORC1, which, in this context, is suggestive of protein synthesis. The researchers hypothesize that the WALK group might have encouraged muscle growth through other means, such as increased blood flow.
A different look at regular exercise
The researchers note a previous study showing that older men who rested for 10 hours after acute physical activity did not achieve significant benefits in muscle mass [6]. While this study involved younger people, it is a credible hypothesis that interrupting sedentary periods might be a key factor in the continued uptake of muscle-building proteins, even among older people. More research will need to be done to determine if ‘activity snacks’, conducted throughout the day, are more effective than simple daily exercise in combating sarcopenia.
Literature
[1] Oikawa, S. Y., Holloway, T. M., & Phillips, S. M. (2019). The impact of step reduction on muscle health in aging: protein and exercise as countermeasures. Frontiers in nutrition, 75.
[2] Wall, B. T., Dirks, M. L., Snijders, T., van Dijk, J. W., Fritsch, M., Verdijk, L. B., & van Loon, L. J. (2016). Short-term muscle disuse lowers myofibrillar protein synthesis rates and induces anabolic resistance to protein ingestion. American journal of physiology-endocrinology and metabolism, 310(2), E137-E147.
[3] Oikawa, S. Y., Holloway, T. M., & Phillips, S. M. (2019). The impact of step reduction on muscle health in aging: protein and exercise as countermeasures. Frontiers in nutrition, 75.
[4] Burd, N. A., West, D. W., Moore, D. R., Atherton, P. J., Staples, A. W., Prior, T., … & Phillips, S. M. (2011). Enhanced amino acid sensitivity of myofibrillar protein synthesis persists for up to 24 h after resistance exercise in young men. The Journal of nutrition, 141(4), 568-573.
[5] Loh, R., Stamatakis, E., Folkerts, D., Allgrove, J. E., & Moir, H. J. (2020). Effects of interrupting prolonged sitting with physical activity breaks on blood glucose, insulin and triacylglycerol measures: a systematic review and meta-analysis. Sports Medicine, 50(2), 295-330.
[6] Bülow, J., Agergaard, J., Kjaer, M., Holm, L., & Reitelseder, S. (2016). No additional effect of different types of physical activity on 10-hour muscle protein synthesis in elderly men on a controlled energy-and protein-sufficient diet. Experimental gerontology, 79, 16-25.
