Heart rate or power? Overtraining?
I often get asked which is best to train to, heart rate or power? Well this is an interesting question, I would say that the ideal is to have access to both. Heart rate alone is not an accurate measure of loading but it does reflect what is going on within the body. It marks, stress, impending illness and can indicate if overtraining syndrome is just around the corner.
Power is a true marker of what your body is able to attain. During a training session you can quickly and easily head for and maintain a target pace or power output, you can work to this and it is a pure workout. What do I mean by pure? I hear you ask yourself. If you were to work to heart rate alone, you will often find that in an attempt to get your heart rate up to the desired zone you will work too hard, reach the zone and bizarrely the heart rate will continue to increase so you then have to slow down or reduce your power by changing gears to stay in the correct zone. This unfortunately does not teach you to pace your efforts, as you have quickly produced lactic acid by going too far over the lactic acid threshold which can only be removed by going easy.
Our bodies produce lactic acid all the time and we must train to be able to tolerate and resynthesise greater amounts of lactic acid, sessions will be designed to help your body to deal with these effects and in time raise your lactic acid threshold. However if you push too hard at the start of the set, your body has to then reduce the pace/power to repay the oxygen debt which limits the bodies ability to adapt to be able to sustain power efforts. The session becomes more of a pure power effort with an aerobic recovery and reduces the quality of the effort.
To cut to the chase, I prefer to work to power or pace but always like to be able to review the heart rate at these paces or power efforts to ensure that the athlete is not on the edge of illness or injury. Another variable that should be thrown into the mix is the RPE (rate of perceived exertion), how an athlete feels during a workout is also important. Unfortunately heart rate, if an athlete is already in an overtrained state can be deceptive. The heart rate can often be lower at a high RPE which can mislead an athlete (especially the highly motivated) into thinking that they need to work harder or do more because their HR is low. This is a dangerous cycle that many athletes have fallen into at their peril, ending up taking weeks or months off training to ensure they fully recover.
Most important thing to pay attention to is your body, if you feel tired, you most probably are tired, if you think it is just a lack of motivation get your kit on and start the warm up, if then you are still not feeling it, go home. Your body needs rest as much as it need to train, sometimes more!