How soon does fitness follow output and effort?

Not an expert, but I've read that it takes at least 10 days to improve your fitness following breakthrough workouts. That's why a lot of folks tend to do short, but intense workouts on a race week just to avoid feeling flat on race day because it's a too late to build endurance at that point.

Of course, day to day gains can be felt simply by a good night's sleep, good nutrition before during and after the workout, proper hydration, and weather conditions. Glad that your body is taking to the increased volume so well. Keep up the good work

Pam

the body adapts very quickly. for example, if you go out and do a 50 mile ride on saturday and then do a 50 mile the following thursday you'll feel the 2nd 50 mile ride to be easier than the previous 50 mile ride. however, full physiological benefits from a "workout" typically have been shown to take anywhere between 2-3 weeks.

I think Steve- is right on.

I did one epic week in my IM training that I did ~27 hours of training which was a little less than double the hours I had been doing. Ideally I would have done it 4 weeks out from IM but do to timing I did it 5 weeks out...to fully absorb it will be another 10 days or so...just about 2 weeks before my IM in time to taper.

I have a coach so I did what he outlined and my run if you are curious was just 7 miles more than the week before most of the increase in time was on the bike.

not quite; from a single session it takes 4-7 days to realize the training adaptations and full adaptations for the same stimulus around 4 to 6 weeks depending on different variables. Is for that reason many experienced coaches choose 5-6 weeks cycles as opposed to the popular (though far from optimal) of 3 on 1 off cycle.

OP - it depends on your fitness level and years training. In general untrained individuals produce greater fitness gains and those tend to occur on shorter periods of times. Trained individuals can get fitness back faster but training gains become incrementally more difficult to achieve the greater your fitness level.

Each time you exercise you increase your fitness but you accumulate fatigue, the difference of those = performance. Hence after a hard session today @ threshold for instance you will be fitter than yesterday but you will be marginally more fatigue and it will take time (24-72 hrs depending on fitness) to recovr and 4-7 days to fully produce the gains from that session. The following week you should be fitter but most likely also have accumulated fatigue from other sessions. As you body recovers and adapts sessions will become easier but if you are following an adequate progression you'll also be pushing a bit more each time hence some sessions will still be challenging. Once you hit a point in which it is taking you longer to recover is time to unload (recover) to fully realize the training gains and start fomr that point.

In short, yes fitness gains are a day by day thing but depending on stimulus and recovery it will take your 4+ weeks to fully achieve fitness gains.