As a Certified Personal Trainer and Pre and Postnatal Fitness coach, I recommend the RPE (Rate of Perceived Exertion) scale when measuring the intensity of your workout. The RPE scale ranges from a scale of 0 to 10, with the range of numbers relating to how easy or difficult a particular exercise is. For example, an RPE of 0 would represent how you feel when sitting in a chair - obviously incredibly easy with no physical exertion at all; while an RPE of 10 is how you'd feel after doing something incredibly difficult with little to no additional energy left for more exertion. I recommend training in the RPE range of 6-7 range.
Now, this can be hard to gauge. If you're like me and do better with more concrete numbers and guidelines, you could also use the RIR scale, which stands for "reps in reserve". This measures the intensity of a lift by describing how many more repetitions you could perform before technical failure (aka the inability to perform the lift with good form or reaching failure). This is a similar 10 point scale but the numbers ranging from 0-10 represent how many reps you have "left in the tank" before this failure is reached. I recommend training in the 2-3 range, meaning if you absolutely had to, you could still busy out an additional 2-3 reps before failing.
Here are some additional ways you can assess if you're lifting heavy/working out hard enough:
- If you are prescribed 10 reps for bicep curls, and you can fly through all 10 reps no problem, the weight is too light.
- If you can maintain a normal conversation for all 10 reps, the weight is too light.
- If you don't need a 30-120 second rest (depending on the exercise) after a set, the weight is too light.
On the other hand,
- If you have to take multiple breaks throughout the 10 reps, the weight is too heavy.
- If you are sacrificing form and/or you end up recruiting other muscle groups to execute the exercise, the weight is too heavy.
- If you can't get the full range of motion for the particular exercise due to weight, the weight is too heavy.
Hope this helps!