Training == Rehab
Typically when injured, hurt, or carrying a niggle the advice is to "rest" - but this could be prolonging recovery. The objective of training is to provide a stimulus that kicks off the body's repair processes - a degree of damage occurs that the body overcompensates for, which then makes us more resilient. These are exactly the same processes that rehab/physiotherapy utilises.
So, if injured, finding a way to train around any discomfort, maybe by using different movements, ranges of motion, or lowering intensity whilst still hitting the affected area can dramatically improve recovery.
Tbh, we rarely ever feel 100%. There will always be aches and pains, sleep can be compromised, life stresses can be higher than normal, etc. - a whole bunch of vectors pointing away from the gym, so getting used to training in non-optimal states can be important for long-term success.
This week I've been fairly sick (not covid thankfully, more a cold). I'm still suffering the effects, but when the symptoms became sufficiently mild, I decided to see where I stood. I had pre-planned targets for the workout, but the idea was to warm up to 10% off that first top set, and if that felt alright, try 5% lower - using the results to guide the remainder of the workout by sussing my capacity for the day.
To my surprise -10%, and then -5%, both moved well so felt comfortable going for the target weight which was 0.5kg heavier than last week. Video shows last week (left - squat: 155.5kg, bench: 100kg) against this (right - squat: 156kg, bench: 100.5kg), and meeting or beating that performance.
This is a workout I would have skipped in the past until I was "better" (maybe in a week or more time?), but clearly, I was already there, even if feeling non-optimal - so, able to continue building on the progress of the weeks before, avoiding a stall or even regression. Dropping 10 or 5% on this would still have been a productive workout if that's where my capacity lay - it's not about the absolute weight on the bar, it's more about working just-hard-enough to provide the correct stimulus dose/response.
Sometimes, the trick can just be showing up, even when not feeling the best, and then taking it from there - and that can make the best medicine.