I’ve had this conversation with numerous patients. We talk about the need for strength development and their response is “I go to the gym already”. I ask them to describe their work out and its something along these lines “20 minutes on the treadmill, 20 minutes on the elliptical and 10 minutes on the stepper”. I’ve come to learn that its a common assumption that anything that happens within gym walls will make you stronger. Here are some key concepts I pass along to patients:
1. Time under Tension
Tension is a major stimulator for strength changes. Enough tension in a focused period of time produced through a muscle contraction and you’ll get a cascade of events that lead to larger muscle fibers. The right amount of tension varies for every muscle and every movement but here is a simple rule of thumb.
With appropriate tension it should be challenging to complete an exercise 10 times
It can be that simple. From the opening example 20 minutes on the treadmill gives about 2000-4000 footsteps (people range from 100-200 steps per minute). To accomplish 2000 steps your body is generating far less muscle tension than is required to stimulate growth and your body uses many passive spring like tissues to supplement the muscle work.
2. Muscles become fuel
A very relevant point about cardio focused training is that if you calorie intake is less than your workout demands you will start breaking muscles fibers down to fuel the run. In a pinch proteins from muscle will give you about the same energy as the same volume of carbs. Once you burn up those energy reserves you’ll switch to a catabolic state when muscles are broken down for fuel rather than built up for strength.
3. Range of motion
The last point about strength is range of motion. Even if we ignored the effects of tension and muscle catabolism, cardio moves you through a very specific motion. If strength gains could be made they’d only apply to that movement meaning it won’t make you stronger to lift that box on to a shelf or smoke someone in a pushup contest.
That’s the usual discussion. If we have time I’d certainly expand on why strength is essential to good musculoskeletal health and the basics of a gym training program.