Is it right that frontal muscles above knee gets tired (don't like it) during bicycling with heightened load (>260W)?

Question

I am doing 15 min cycling each day at home and each time I try am putting maximum load (by regulating load and decreasing RPM) for periods of 1 minute and 1.5 minute. I am keeping 85-90 RPM at these loads and makes sensors to report 280-330 W load. It is a bit heightened load. But I have this idea that such heightening is good for me, because:

• It is said that one should achieve the state of sweating and gasping during workout - only by achieving such state the health of heart improves. Just walking (even large distances) or just lifting weights without seating and gasping is no especially worth for the heart;
• I just want to keep my muscles fit and my guess is that they should be exposed to the heightened load for this.

So - that is my rational for the heightening of the load during cycling. The problem is - that the frontal part (approx 5-15 cm above knee) of the leg above the knee gets tired during such workout episodes. And I don't like this sense of tiredness. It is not hurting, it is not creating some physical discomfort, it is just signal of tiredness in that place, in both lets.

I wonder - what muscles can be there? My guess is that there are very few muscles and they should not be important for the cycling. But still - this tiredness is the one single cause why I am not happy about cycling and heightened load and why I should press myself for my daily routine of cycling. When the load is under 240 W, this tiredness disappears. My base load ir 180-200W (at 90-100 RPM), I am not going below that.

So - my question is - is this sense of tiredness normal? If it is normal then how to cope with it psychologically? And if it is not normal - then what I am doing wrong? How others experience this?

But maybe there is physiological sense in such sense of tiredness - maybe it is in the interests of the body to keep such vulnerable (but insignificant) muscles with inform about achieving maximum possible load and in such why the body may prevent that maximum load is exerted e.g. on the heart and that prevents the heart to be the weakest element of the chain which should report achievement of maximum and which may experience the harm due to it.

For years I had this sense. Absolutely no problems with the knees themselves. Only now I am asking this.

My body: 185 cm, 95 kg.

Answer 1

I wonder - what muscles can be [approx 5-15 cm above knee]? My guess is that there are very few muscles and they should not be important for the cycling.

That would be the quadriceps, and they are definitely very important for cycling.

What you are most likely experiencing is hitting your lactate threshold - the power level at which your body cannot provide enough energy to your muscles via the aerobic energy system, making you reliant on the anaerobic energy system. The anaerobic energy system creates acidic waste products in the muscles being used, which causes fatigue and a "burn" feeling in those muscles. The fact that the discomfort reliably begins at a certain power level also supports this explanation, and 240W would be a realistic threshold for a casual cyclist.

So your options are to either endure the discomfort of training at this intensity, or reduce your intensity to 240W or less. If you were to do 15 minutes every day at 240W, that would probably only just satisfy the cardiovascular portion of the World Health Organisation's physical activity recommendations, which are at least 75-150 minutes of vigorous intensity exercise per week. 15 minutes per day is 105 minutes per week, and vigorous is roughly defined as an intensity where it would be difficult for you to hold a conversation.

So cycling at 240W would still be beneficial and worthwhile, but incorporating at least some higher intensity training would probably be more beneficial.