Whether you are new to exercise, out of shape, recreationally active or an elite athlete looking to maximise your performance, the way our muscles respond to exercise are similar. Should you partake in some exercise today, be it a walk, run or a strength training session, you will stress your body in some way and this will initiate a response. Exercise impacts a number of organs within the body by disrupting our resting state. For example, we see immediate changes such as an elevated heart rate and blood flow to key areas of the body including the muscle, brain, liver as well as increased metabolism in other tissues. For the purpose of this article, we are going to focus on the impact of exercise on our muscles.
How does exercise impact our muscles?
We have all been that soldier during or after an exercise session where we have pushed the body to or near its limits and said “Woah! That was tough”. Given the choice, we may have liked to go faster or further, but we were simply not capable and are likely to feel the effects as we recover over the next 2-3 days with potential fatigue and soreness. This marks the early stages of the response in our muscles which will ultimately lead to us getting better at exercise. Our muscles are very clever and respond effectively by saying “I wasn’t ready for that. If you ask me to do that again I will be better prepared next time. What did I not have ready that I need for the next day?”. The muscle then goes about putting those support systems and infrastructure in place. To explain this better, let me provide an analogy.
Equate our current exercise ability or “capacity” in terms of our recent vaccine rollout programme, i.e. our ability to administer X number of vaccines per week represented as our “vaccine capacity”. Many of you will recall January 2021 when we looked enviously at the UK and bemoaned our own vaccine rollout when we were administering a paltry 1000 vaccines per week. That is the equivalent of an unfit or out of shape muscle. That “vaccine capacity” was so low because the infrastructure and support systems were not yet in place, limited by factors such as vaccine supply, our number of vaccinators, cold storage, vaccination centres, IT and software infrastructure, and so on. Once we identified each week what was limiting our rollout, we could act on it, put the necessary tools in place and ultimately build our capacity to the point where we were rolling out 250,000 vaccines a week by Summer 2021. That efficient system is the equivalent of a trained and fit muscle.
When our muscle lacks the necessary infrastructure it too has limited ability. Following a single session of exercise the muscle will go about building that infrastructure to ultimately enhance our exercise capacity. This involves building the machinery in the muscle which allow it to contract and dictate the amount of force it can generate, increasing our supply of accessible energy and the number and efficiency of the compartments where this energy is generated. This requires remodeling of the muscle by breaking down old and generating new proteins. Exercise acts as the stimulus which initiates these processes.
Building our muscle’s capacity
In the nucleus of our muscle we house our DNA or genetic library, a recipe book if you like, for the different genes which give us the code for proteins we need. We make a copy of the codes that we need to make new proteins. These copies are known as messenger RNA or mRNA for short. Research at the University of Limerick shows that this process begins immediately and we see an increase in these gene copies in the muscle, peaking around 3 hours after even one session of exercise. We then ‘translate’ that code to assemble the right combination of amino acids which are the building blocks of new proteins. Each of these new proteins that we generate has a specific function. Some will improve our ability to produce accessible energy to fuel exercise, others will enhance our ability to create larger forces. Ultimately, this new infrastructure and support system provided by these new proteins will improve our exercise capacity, making us fitter, faster, higher, stronger!
Why is this important?
You might be surprised to know that muscle is the largest organ in the body, accounting for approximately 40% of our body mass. Muscle is extremely important for our daily living and independence. In fact, the strength and function of our muscles is an indicator of not only our lifespan, but also the period of life spent in good health. Muscle is also interesting as it is a very metabolically active tissue which is important for our health. For example, the muscle acts like a sponge for blood glucose or sugar which has implications for metabolic diseases such as Type 2 Diabetes. By maintaining our muscle size and health through exercise, this helps to regulate the level of glucose in our blood following a meal or snack. Even a single session of exercise reduces the spike in blood glucose that we see around meals such as breakfast and across the entire day.
Knowing how the muscles respond to exercise enables us to understand what changes are happening which lead to improved performance and health. This has implications for not only athletes, but also for the potential prevention and treatment of diseases such as Type 2 Diabetes, Cancer and heart disease.
If you haven’t already, I suggest doing some exercise and building some new proteins in your muscle today. Your muscles will thank you for it!
Dr Brian Carson, PhD; is a Senior Lecturer in Exercise Physiology; firstname.lastname@example.org in the Department of Physical Education and Sport Science in the University of Limerick. Dr Carson is interested in metabolic adaptation in response to exercise and nutrition.