How hard do you have to exercise, is there a magic number?

In a former life I used to throw things, specifically hammers. I did alright but I was always chasing a magic number.

That number was 70, well 70 meters and more was what I really wanted,  but unfortunately I didn’t get there.

However it got me thinking after doing some research into exercise and rehab that maybe 70 is a magic number and also there are lessons I learned from not hitting that magic number with the hammer.

What do we mean by 70 being the magic number for exercise?

To set the scene, when dealing with prescribing exercise, whether its lifting weights or doing cardio we tend to express the intensity we exercise as a percentage of our maximum ability.

So in terms of exercise we are looking at 70% of maximum effort.

How do we exercise or work out  70% of our maximum effort?

In terms of rehab we don’t have to get to scientific as there are some fairly simple tools you can use to get to that 70% level. The simplest of these are the OMNI resistance scale.

This is a self measuring scale on how much effort you feel you are putting in to that form of exercise.

7 out of 10 is the start of the sweet spot.












If you are a more seasoned trainer and have the equipment you can determine cardio based worked outs off maximum heart rate or weights you have lifted in the past. Either as a direct percentage of your best 1 repetition maximum lift or via an equation such as the one below:

Weight lifted x repetitions performed x 0.0333 + weight lifted = Maximum x0.7 = 70%

for a deadlift of 100kg x 3 reps we would calculate 70% level as follows:

100kg x 3 x 0.0333 +100kg = 110 x 0.7 = 77kg

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Why is 70 a magic number for exercise and rehab?

This will come as no surprise but the tissues and systems that comprise the human body are essentially a single entity. They are not distinct separate entities operating on their own.

As such its not too big of a leap to suggest there may be an optimal intensity of activity, whether it is cardio or strength based, that has positive effects on the health  and fitness status of the tissues.

Lets look at tissues and issues we commonly deal with at the clinic:

Muscle strength & exercise:

building muscle: curls get the girls ?!

When it comes to building muscle (hypertrophy), the magic really starts to happen when we are training at the 70% level.

However if an individual has no experience of weight training we can get similar results at 50-60% level. This is why beginners in a gym will see such large improvements that taper off the more you continue.

It doesn’t matter how old you are you can always improve on your strength.


This is an important factor in rehabilitation to those who have suffered:

  • Direct muscle injury or sports related injury.
  • Post operative patients who have lost muscle mass.
  • Over 60″s population who are at risk of developing Sarcopenia... Loss of muscle mass which has huge health implications.

Recommendations for muscle building : 7-12 repetitions at 70%-80% intensity, 3-6sets (adapted from Kraemer et al 2002).

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Tendon & strengthening exercises:

achilles tendon
Achilles tendon, common site of overuse injury

As tendon and muscle are intimately related for function it is unsurprising that the 70% figure applies to tendon. In a review looking at the effects of resistance training and tendon adaptation researchers found the intensity of force or load required for adaptive change in the tendon was from 70% of maximum and above.

They also determined that this was the most significant factor in the strengthening of tendons. They also showed that training for periods of longer than 3 months was more beneficial than 6 weeks or less.

This does not mean though that tendon pain will take months to resolve, exercise can have a fairly quick pain relieving effect.

Recommendations: using a similar scheme as seen with muscle is a pretty safe bet.

Bone strength & exercise:


This is where the magic number rule is close but not quite on the mark.

There have been benefits shown in bone density at around the 70% mark however it is recommended that 80% -85% is probably more the magic number for increasing bone density.

However you need to hit that 70% mark before you get to the higher numbers.




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  Nerve pain and exercise :

There is a growing body of evidence that exercise decreases symptoms of acute pain in humans and has been is known to have an  anti-inflammatory effect, and reduce neuropathic or nerve related pain in rodents.

A study on rodents (again), has shown that performing cardio based exercise at around 70% of V02 maximal effort resulted in significant changes in nerve related pain and increases in the bodies own natural anti-inflammatory chemicals.

Focus on the process, not the outcome.

If I was to pick the major lesson from the throwing field as to why my initial quest for 70 meters was unsuccessful it was that I focused on the outcome and not the day to day process of getting there.

Start small and build up to the level.

It may take time to get to the 70% threshold so you have to plot a path to getting to that level of intensity that:

  • Minimises set backs.
  • Allows the body and tissues to adapt to new stresses and forces.
  • Learn new skills.
  • Build your confidence in the movements.

Luckily if you are new to exercise your results will come quicker as 50-60% of your max effort will start to reap results.

Those of you who have experience with exercise will probably find the path to that 70% level easier to get to. The body doesn’t forget.

So these are my thoughts on how hard we need to exercise to get the results we deserve.

Cheers Dave

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(Dave is back pursing his dream of throwing 70 meters much to the bewilderment of his family and now has a back garden looking like the surface of the moon.)


Fundamentals of Resistance Training: Progression and Exercise Prescription. William Kraemer et al. Medicine & Science in Sports & Exercise. Vol. 36, No. 4, pp. 674–688, 2004.

Human tendon adaptation in response to mechanical loading: a systematic review and meta-analysis of exercise intervention studies on healthy adults. Bohm et al. Sports Medicine – Open (2015) 1:7

Effects of Resistance Exercise on Bone Health. A Ram Hong , Sang Wan Kim. Endocrinol Metab 2018;33:435-444

Exercise Training Attenuates Neuropathic Pain and Cytokine Expression After Chronic Constriction Injury of Rat Sciatic Nerve. Yu-Wen Chen, PhD.  ANESTHESIA & ANALGESIA. June 2012 • Volume 114 • Number 6