- Nov 14, 2003
Originally posted by 2LAP
This is a really interesting question!!!!
This is most likely to be caused by local muscular fatigue and neurological factors (hence you can't press that hard on the pedals to raise your HR) as your nutrition and hydration is OK. At the start of the ride you will be recruiting a number of motor units (i.e. groups of muscle fibres) and as these fatigue additional units will be recruited. By the end of the ride you will have few 'fresh' motor units to recruit and so have to slow down or won't be able to lift the pace. This has muscular and neural origins and means that you can't contract the muscles forcefully even when you can still produce ATP at a good rate (i.e. not glycogen depleted).
Also, your central nervous system also fatigues, which means that it doesn't provide the same number of nerve impulses that it could at the start of the ride. You can measure this change in a lab using EMG. It is caused by changes in the neurones themselves and also by hormonal changes in the body and brain.
Could you explain these neurological and central nervous system factors a bit more, or provide some references I might be able to get on pubmed? Sounds interesting. Thanks.