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If the heart rate cannot be kept in the basic zone during GA1 (basic endurance 1) training when increasing the duration of the load, should the training then be continued with a reduced wattage or increased heart rate?

Basically, the following applies: In the GA1 zone, you should control your training according to heart rate, in the GA2 zone according to heart rate and/or power output, and at higher levels of intensity only according to power output. The pulse rate is too sluggish to respond to the rapid increase in power output during intervals or when training in the development zone. In the basic zone, however, it reflects the current overall load on the body really well.

If your heart rate increases at a constant power output during long GA1 training units, this is initially due to a change in your metabolic state: If the carbohydrate reserves are progressively used up, the body needs to ramp up the lipid metabolism. However, in order to obtain the same amount of energy from fats as from carbohydrates, the muscle cells need more oxygen. This means: More oxygen at the same power output, which requires the heart to transport more blood and beat faster.

In addition, the body can get overheated in poor climatic conditions. As a result, blood from the muscles is diverted to the skin to cool down. This also means extra work, which results in an increased heart rate at the same power output. This effect can intensify if you do not drink enough. You sweat more indoors and therefore need more fluids than outdoors.

Normally, an increase in heart rate by 10 to 15 beats per minute during longer basic training units should not be seen as negative. However, if the values increase even further, it is right to reduce the power output in order to prevent excessive heating.