Re: Muscular response to physical exercise

Hello Gaby,

I find your question very interesting since it is not something I have been 
aware of in the general population until I read your question but it has 
got me thinking about my own father, who despite being a very keen 
sportsman and extremely fit, having played a variety of sports throughout 
his life, has always been a hopelessly bad swimmer and as much as he tries 
gets tired very quickly when in the pool. 

However I do not know what causes this but I do have some ideas for 
possible causes.
Firstly the people that you describe are physically fit and exercise 
regularly.  If a person is physically fit then they should be able to 
perform any form of exercise to a reasonable level and I don't think that 
it is an effect of general fitness.

In the case of my father I would say that this is partly down to a poor 
swimming technique that is inefficient and without a regular breathing 
rhythm. Swimming requires a mixture of upper and lower body strength since 
it uses the arms and the legs and the co-ordination of the two to work 
efficiently together with a regular co-ordinated breathing pattern.  If an 
individual finds it difficult to co-ordinate all these simultaneously then 
their swimming style may be inefficient, resulting in the person tiring 
quickly.

Another possible reason is that different exercises use different muscles 
or the same muscles differently.  For example running trains leg muscles to 
contract quickly on impact with the ground but does little to train the 
upper body.  The action of swimming is obviously very different from 
running where the muscles are used in a more sustained type of activity.  
Muscles adapt to particular exercises.  Muscles contain a number of 
different fibre types; fast twitch fibres that work very quickly and slow 
twitch fibres that work more slowly.  Running is definitely a fast 
exercise, but swimming may require more of a range of fast twitch than 
slower twitch fibres.  During training the muscle will adapt and produce 
more of the muscle fibres that needs for the activity for which it is being 
trained and the fibre types that are used less will become fewer relative 
to the trained fibre types.  So muscles that are trained for running may 
not be so efficient at swimming activities.  However, if a person then 
swims regularly then the muscle should adapt to this. 

A third possible reason that I can think of is buoyancy.  Buoyancy is 
dependant on the physical make up of a person, amounts and distribution of 
body fat will be important for example since body fat helps people to 
float.  This may also be a contributing factor for ones ability to swim.  
If the swimmer has to spend more energy not sinking whilst swimming then 
this will also affect the efficiency of the swimming stroke.

In summary these ideas all indicate that it is most likely  an effect 
relating to the efficiency of the swimming stroke that you are describing.

Thank you for you very interesting question.  I am afraid I am not aware of 
any literature on this subject that I could point you in the direction of 
and I am not aware of any studies that have been done to investigate this 
but it is a very interesting observation. Good luck in the future.

Dr David Burton