All body tissues that are part of movement can adapt over time based on the stresses you put on them (your bones, muscles, heart, lungs, etc). This can give us lessons for thinking about the things that we once were able to do.
Activities that were once a good challenge when we moved more regularly may be very hard now or even cause an injury if your body has not needed to meet the same high level challenge in a long time. It is good to start at a lower level of difficulty (start low) and add new challenges slowly (go slow) at any age! Very early strength gains will come as your body becomes more efficient with repeated movement, but true gains will take repeated training at a moderate challenge. What's exciting is that what you consider a moderate challenge will change over time as your body adapts to your demands!
Is there a certain level of challenge that is best to build muscle strength and function? Yes, there is. Technically, to build strength, you must challenge a muscle to work 60% of its maximum capability. How do you do that? Start by using 20 repetitions of an exercise to help guide you. If you can perform an exercise (think of simply bending your elbow) 20 times without growing tired or without need to decrease or change the motion then the exercise is too easy to build muscle.
If you bend your elbow 20 times while reading this section you can answer these questions:
- Did you have to stop or lessen the full movement or change the position of your arm to complete the count of 20?
- Did you need to stop the activity to relieve a sense of burning in front of your upper arm above your elbow?
If you answered no to both of these questions then the weight of your lower arm against gravity is too low a load to build muscle strength in your upper arm muscles.
60% of maximum capacity means that you are feeling fatigue (often a ‘muscle burn') or you are no longer able to complete the full movement by the 15th repetition.
You may think, if lower than 15 repetitions is good then maybe I should go even lower. If you challenge yourself to tire out your muscle in less than 15 reps you will be using more of your muscle capacity with each exercise, but do be careful – remember the go slow part! Using our example from above you can bend your arm with a bag full of groceries. It will tire your muscles faster, but it can also make you very sore. Another important point is that people may have a hard time controlling their body position when challenging themselves to a very high level so if not done properly it may lead to injuries.
Let's work through another example using your legs. Let's say rising from a chair is a challenge and you want to perform a sit to stand exercise from your chair. It may be too great a challenge to perform 15 sit to stand exercises, but you can make the challenge easier by partially sitting down and rising again (called a partial squat) 15 times before tiring your muscles. This makes sure you're still working your muscles, but not losing control of the exercise movement. As you grow stronger you can start to squat deeper to increase the challenge. As you grow even stronger, you can do the movement with small weights (or bottles of water) in your hands.