One of our clients during her workout last week asked, "What causes the muscles to tire during exercise?" This is a great question, as we all experience muscle fatigue during our workouts. You will be in the middle of a set when all of a sudden, there goes all your strength and no matter how you try you can't perform one more repetition.
Unfortunately this is not an easy question to answer. In fact there are whole books, not just chapters written on effects of muscle fatigue and how to deal with fatigue during sport performance. Obviously one of the limiting factors in any sport activity is the loss of strength, power or speed in a muscle. This area of exercise physiology is constantly being studied and new discoveries on how our muscles work are happening constantly.
If you did a Google search on muscle fatigue you would find thousands of sites or articles dealing with muscle fatigue. If you then did a search on muscle fatigue and exercise you would also find literally thousands and thousands of sites and articles dealing with fatigue and how it relates to exercise.
Muscle fatigue is a very complex series of chemical, neurological and physical actions that occur during exercise or activity. In doing an on line search for definitions of muscle fatigue this is what I found:
- A condition resulting from prolonged and strong contraction of a muscle.
- Studies during prolonged submaximal exercise have shown that muscle fatigue increases in a near direct proportion to the rate of muscle glycogen depletion. Muscle fatigue in short-term maximal exercise
is associated with oxygen deprivation and an increased level of blood and muscle lactic acid, and an accompanying increase in hydrogen-ion concentration in the exercised muscle.
- A decreased capacity to perform a maximum voluntary muscle action or a series of repetitive muscle actions. A fatigued muscle is unable to continue working even when the type of activity is changed. Muscle fatigue may result from depletion of
phosphocreatine or glycogen, accumulation of protons generated by lactic acid, exhaustion of neurotransmitters, or some other mechanism.
Here is a link to an excellent article that goes into more detail about muscle fatigue. This excellent web site has several links that you may go to to help explain the relationships around muscle fatigue physiology.
So, bottom line what does all of this have to do with your sessions at the gym. After all that was what prompted the original questions – why do my muscles get tired when you work out? You may read through the Sports Medicine links in more detail, but simply how I look at in the gym….
We all get fatigued in the gym. As we perform a set of a specific exercise whether it be bench presses, squats, lunges – doesn't matter, the muscle will get tired and if you read any of the physiology you will realize there are many factors at work from depletion of ATP, lactic acid accumulation, etc. But for me, I don't think so much about the physiology – calcium ions, lactic acid, hydration factors, stress, etc. I just try to focus on doing the best I can each workout. Some workouts are going to be great and you will wonder what did you do to have such a great workout? What did I eat for dinner the night before, how much sleep did I get? The questions are endless and if you could figure that one out and bottle it – well are your worries financially would certainly be over.
If you think back to when you first started training at the gym, your weights were a lot lighter than they are now. The exercises were simpler, not as complex or demanding. And the repetitions were probably higher with lighter weights. But the reasoning for that is a whole other article.
What I try to think about when I am performing a set is to do as many as I can with perfect form. Some days that set of lunges may be 8; some days it may be 6 and some days it may be 10. Overall, though you will find a consistent number that you will be able to perform with good form before muscle fatigue sets in and your form will be compromised and that is where your trainers will step in and usually stop you.
I think one of the hardest things for people new to weight training to learn about, is when to push and what the "burn" is all about. This once again could lead to a whole new article or even a book. It is okay to feel the burn in the muscle; this is the muscle working and it not about to be injured.
Sharp pains are to be taken seriously and definitely any pain close to a joint needs to evaluated, but the burning sensation in the muscle is okay. This burning sensation will stop once the exercise has ceased. This sensation in the muscle is not usually an indication to stop. Most of us will usually be able to perform 1-2 or more repetitions when this burning starts.
I realize I have probably got a little bit off topic here. It is hard to talk about muscle fatigue without starting to talk about training programs, exercises, sets and reps.
I think it not so much that we need to know what causes muscle fatigue. It is interesting to understand the physiology around muscle fatigue, but what really counts is the consistency of your workouts and the effort you put forth when you go to the gym.
Muscle fatigue is expected and even welcomed. Recovery is the next important step before returning to the gym to enjoy another great workout.
Till next time,