Legs burning when they shouldn’t be?
"When I started the workout, I could tell my legs were not feeling great. The only word that came to mind was "toxic" - It was hard to get through the warmup, including the first reduced-intensity set."
Here's what might cause early-workout leg burning:
Faster than optimal ramp during warm-up.
Acute fatigue from recent session.
Non-acute fatigue from training volume.
Dehydration/fueling issues.
Fitness loss.
Usually, it's numbers 1 and 2. Sometimes numbers 3 or 4 play a role. It's exceedingly rare that this leg feeling is related to number 5, and if it is related to number 5, it's still MORE related to at least one of the other things above it.
I think I can count 2 cases out of 1500 clients where I assessed that, "yep, this person has lost fitness, and paired with numbers 1 or 2 and 3 and 4, the overall interplay was the crux here."
All other cases, it's just not fitness. This should put some minds at ease.
The easiest reason to conclude it's not related one's fitness is that fitness is harder to lose than most people think, with even very low training volumes. Maintenance training volume is lower than most people think.
It's much more likely that poor performances are explained by fatigue, hydration, fueling, or other factors that can affect performance, outside of physiological fitness.
All of those but fatigue are fixable with a few minutes of concerted fueling, hydration, or caffeination.
I tell you all this so that you can quiet that voice in your head that says "have I lost fitness?" or "is my fitness down a bit today?"
Immediately take action
Extend and slow down your warm-up.
Drink & fuel.
Caffeinate if you feel "down."
