Your picture helps me Fergie Fulton, to figure out posture, hand placement, and very nice looking Squier there too.
What is this about diet, bass players take for granted? I remain curious from the 1st page you posted...
That picture is just a moment caught in time, it shows nothing of where that position came from or where it was going. Part of the job is to entertain as well as play and the two do not always compliment each other in terms of what is best for either. The bass is a JV 1983 early model of the 57 Precisions they made..perfect in every detail apart from not made by Fender in 57
The diet of a musician needs to be able to provide energy for the muscles through Carbohydrates, and protein to aid the brain to be alert and responsive.
In playing bass the task is the physical one of the muscles playing, and the mental one of the brain being focused, but keeping out the way.
In learning or in practice, the task is still physical, but now the brain needs to concentrate on learning....not remembering.....but learning.
Take the instrument away and the simulate the hand movement to play...it is physical, therefore the muscles producing the movement need energy.
Because we do not have the usual features of physical exercise, raised, deep and quickening of breathing, sweat, increase in heart rate etc...does not mean that the muscles are not using energy, they are but rather than the source being aerobic ( oxygen based ) in is anaerobic ( non-oxygen based ) to trigger the bodies metabolism to react.
So when playing for a long time and the hands tire, it means the body is fatigued and needs energy.
But what ifI have just started to play and I am tired? *Well it is the same thing fatigue....the body needs energy, a source of fuel if you will.
Whether you start to run out of body fuel through use or just did not have enough to start with will bring the same results of tiredness, cramp, and the inability to concentrate or be alert as well as you should.
So the energy or fuel will come from diet.
So energy bars and drinks are a good temporary source to give a boost though out playing or practice. That is a eating or drinking them at regular intervals through out the activity. Having good hydration levels by taking in water or those energy drinks is a vital one as muscles need water to help them work effectively.
Many players find themselves working in bars and clubs where alcohol is served, and in many cases is offered as part of the deal. Alcohol dehydrates and since the body needs water to function alcohol is not a good mix for the body or the brain in order to perform the task of playing.
Sure it may take the edge off, but that may just be a release of serotonin from the brain, that feel good chemical that is released when we enjoy something such as chocolate, pizza, etc.
Of course this scene of bars, clubs, the times they open etc, will bring us in contact with fast or junk food. Processed food is OK once and a while ( that serotonin kick is involved again ) but it is not a balanced healthy diet.
A balanced healthy diet means our bodies are ready to function, our brain is alert and all we need is to top up a little in order to function at certain tasks for certain periods of time.
This brings us back to playing bass.
So practice did not go as well, maybe you were tired and not thinking as good?????????
Playing that gig did not go so well...again maybe you were more tired than you thought...maybe your mistakes were mental ones because you could not focus on the song or the arrangement, this causes a panic as you move out your comfort zone, the body tenses more, the movement become less, now you are thinking about what you should be doing, rather than doing it ( the brain is in the way ) and so on.
Quite simply diet gives us the energy or fuel to function, since playing is a raised function ( an extra level of you will ) then fuel intake has to reflect this...in other words you need more in the tank to do it. Just sitting down and start playing will not work as well as preparing or being prepared to play. As will just turning up at the gig and going for it not always work as well.
So get a balanced healthy diet, and always make sure you are prepared to play by being hydrated and having eating a good energy source ( carbohydrate and calorie rich food for that extra energy ) as a top up about half an hour before playing, and the body will take care of itself leaving you free to play.