Measuring muscle strength

How do you go about finding just how strong you are in a particular exercise?

You could try using larger and larger loads until you reach the limit of your strength – but this is dangerous because, if you try too great a load, you could strain or tear muscles and tendons.

This maximum strength you are trying to measure is given the name one repetition maximum (1RM). This is a measurement of the greatest load (in kilograms) that can be fully moved (lifted, pushed or pulled) once without failure or injury.

This value is difficult to measure directly because the weight must be increased until you fail to carry out the activity to completion. Because of the high chance of injury, this activity should not be carried out and measured with untrained people.

So, it is safer to estimate 1RM by counting the maximum number of exercise repetitions you can make using a load that is less than the maximum amount you can move. This number is called the repetitions to fatigue (RTF) – you stop counting the repetitions when you can no longer perform the exercise properly or when you slow down too much and cannot keep a steady pace.

A person’s 1RM will be different for each kind of strength movement. For example, in research this year at Auckland University of Technology (AUT), twelve elite yachtsmen from the Emirates Team New Zealand America’s Cup squad were measured to have an average 1RM of 119.7 kg for the bench press and 99.4 kg for the bench pull.

One benefit of calculating your 1RM for various strength movements is that you then know a limit below which you can safely train.

1RM can also be used as an indication of your strength development. Because 1RM will vary according to muscle strength, most people who are undergoing strength training will repeat this measurement at regular intervals to find out if they are gaining strength.

How can you estimate 1RM?

The values of the load you used and the number of repetitions you counted (the RTF) are entered into a prediction equation that calculates an estimate of your 1RM.

One prediction equation for 1RM that was published by Epley in 1985 has the formula:
1RM = (0.033 x RTF x load) + load

So, if a person can lift a 50 kg weight for nine repetitions before tiring significantly, their estimated 1RM is:
1RM = (0.033 x 9 x 50) + 50
= 14.85 + 50
= approximately 65 kg

This means the person should just be able to lift 65 kg and no more. It also means they would need a rest of several minutes before they could lift the same weight again.

There are a number of equations that have been constructed by other sports science researchers over recent years to estimate 1RM and a number of calculators that use various 1RM prediction equations have been developed – search for them online using the keywords “1RM calculator”.

The sport science community is debating the accuracy of estimating 1RM. For example:

• A person may become familiar with the technique and therefore have an advantage over a person with no experience.
• Does a self-made decision of no longer being able to carry out an activity lead to a valid 1RM measurement?
• Does carrying out an activity with fixed weights provide an advantage over someone doing the same activity with free weights?