Blue zone (Level 1) heart rate indicates that your body is drawing the majority of its energy from the aerobic energy system. The intensity is low enough that your breathing is controlled and there is no burning sensation in your muscles. Zone 1 is utilized during the warm-up, rests and cool down.
- Energy System: Mostly aerobic
- In Level 1, I feel: Like I could continue at this intensity for an hour without a problem
Green zone (Level 2) heart rate also indicates that your body is drawing a majority of its energy from the aerobic energy system. The difference between blue zone and green zone is a slight increase in intensity. Green zone is utilized during steady state periods and recovery.
- Energy System: Mostly aerobic but drawing some energy from anaerobic system
- In Level 2, I feel: Like I could continue at this pace for an hour without a problem. I am sweating lightly now and my body feels warm.
Orange zone (Level 3) heart rate starts to bring us closer to your anaerobic threshold. This is the point of exercise where the intensity reaches a point where energy produced by the aerobic system is not able to keep up with the demands needed. The anaerobic system is able to produce energy immediately but is less efficient and has a byproduct of lactic acid and carbon dioxide (muscles burn and breathing becomes labored). In the orange zone, you will feel uncomfortable but it is here, at this intensity that changes begin to occur in the body. Depending on your level of fitness, you will be limited to how long you can continue at this intensity.
- Energy System: Primarily anaerobic with some aerobic
- In Level 3, I feel: Like my muscles are burning and my breathing is labored. I am not able to keep this up much longer.
Red zone (Level 4) heart rate should only be used by advanced participants. At this level of intensity, heart rate response is slower and it is much harder to maintain the intensity. In this zone, you will be very uncomfortable and muscle burn and or breathing is at a high level.
- Energy System: Mostly anaerobic with little to none aerobic
- In Level 4, I feel: Like there's no way I can continue this pace/intensity longer than 10-30 seconds. I don't like my coach.
If you wish to determine precise numbers to use as thresholds for these zones, you can use the formulas described in this article