There is ample evidence around to demonstrate that a concerted period of low-intensity training volume, well within your comfort levels, results in significant increase in CAPILLARISATION within the trained muscle. There is also ample evidence showing that the body thrives best in a slightly alkali environment, as opposed to slightly acidic. (Think milk versus vinegar, although in fact milk is itself still very slightly acidic, yet relatively far more alkali than vinegar, to be pedantic).
Prolonged high intensity training without due low intensity for recovery has been known to elevate ACIDOSIS in the body, which in turn mucks up cell membrane walls, lowers immune response, and mucks up normal fatty acid and carbohydrate metabolism, as well as the highest-energy alactic energy system. So everything will be run down or working poorly, and will need days to recover.
‘Synaptogenesis’ (the formation of new synaptic connections within the neuromuscular system) and ‘Angiogenesis’ (the budding of tiny new blood vessels which eventually become capillaries or even larger venules and arterioles) are far more likely to occur in an alkali environment. Intense training can promote a powerful stimulus for angiogenesis, however this will only really occur if the whole system is allowed to recover adequately. The same for synaptogenesis. With intense training, and the necessary very very easy days to recover, you’ll lose a lot of steady aerobic work time, and all the benefits that come with that aerobic fitness background.
There is absolutely no point in doing faster, more intense work until a modicum of essential, basic fitness has been acquired. This basic fitness would include good tendon strength and elasticity, and a highly developed capillary system that literally “irrigates” the muscles with fresh oxygen, glucose, and fatty acids, and transports the byproducts away quickly.
Once this basic fitness has been acquired, it can be increased methodically over a number of weeks by deliberately running ‘solidly’ for up to an hour once or twice a week at a level that can be described as “strong” or ‘high aerobic’. Build up to the hour steadily in increments of a few minutes each time from a starting level of around 20 minutes within a 1 hour run. The body seems to like variety in its aerobic training, so we include longer slower runs and shorter steady runs on varying courses each week as well. These runs are also known as ‘3/4 effort’ runs in Lydiard terminology. They are also known as ‘sub-threshold’ runs because they are not supposed to be anaerobic at all.
If you carefully build your aerobic base and your training tempos the Lydiard way, eventually you’ll train your body to burn its relatively vast fat stores for energy, instead of your limited carbohydrate stores, and you will be running strongly after 2 hours of running at your own comfortable pace. Then you will be ready to introduce slightly stronger efforts on specific days, and recover from them each time, as you prepare for a personal best performance.