Aerobic Capacity

These thoughts were in response to a number of recent posting on aerobic fitness, EPO production and cross-training posted on teh surfski Yahoo! group.

Aerobic fitness consists of two main components;

• central cardiovascular fitness (heart and lungs), and
• peripheral (the specific muscles involved in the sport movement)

You can train the central cardovascular system using pretty much any cross-training methods you like as long as you can stress your cardiac function and ventilatory system to a greater extent than you will need in the sport for which you are training. As many previous posts have mentionned running is an excellent form of cross-training through which to develop the cardiac and ventilatory part of the aerobic fitness necessary for paddle sports. Some of the important rate limiting factors in central cardiovascular fitness are;

• cardiac output: the amount of blood pumped per minute which is a function of stroke volume (blood pumped per heart beat) and heart rate (beats / minute)
• blood volume: dehydration or other factors affecting volume will reduce effectiveness of the cardiovascular system
• red blood cell count and O₂ carrying capacity
  

The peripheral adaptations required for aerobic (or anaerobic or alactic) fitness all take place in the muscles and associated nervous system. As such, cross-training has much more limited impact of this portion of training. The changes in muscle architecture, structure,
biochemical composition, etc are all very localized and specific. If the muscles used are similar in a cross-training activity there will be some benefits. However, not only the muscle groups, but also the sequencing of contractions, force of contraction, speed of contraction,
power output, duration of exercise, work to rest ratios and many other factors all have to agree to see mutually beneficial training effects. Two of the biggest rate limiting factors in peripheral aerobic fitness are;

• the ability of the muscle to remove and use oxygen from the blood, and
• the ability of the muscle to maintain a balanced pH (specifically minimize acidity build up which will delay the onset of fatigue).
  

So the answer to whether aerobic fitness is transferable, the answer is yes, no and maybe.

For the poster who observed his running HR was much higher than his paddling HR, this may be explained a number of factors;

1. you probably have a good aerobic power and aerobic capacity in running,
2. your paddling training has not advanced to the same level (both interval training and base work),
3. with systematic inclusion of intervals and base work, both your peak paddling HR and the % of peak HR you can use when in long distance events will increase. Your paddling technique is such that you use a smaller amount of muscle than when running,
4. when you learn to use legs as prime movers and sequence the movement from core to periphery you will see you HR increase to near running values.
5. it may be you are fatigued and unable to increase your HR to higher values due to systemic fatigue, this would only be true if your running values were also decreased at the same time.
   

There was also a comment about O₂ desaturation. High levels of VENOUS (think used) blood desaturation is prefectly normal, and very often blood returning from highly activated muscle is significantly desaturated (well below 50%), as it mixes with venous blood returning from non-working muscles and organs, the % desaturation levels return towards normal. If O₂ levels drop far enough and the lungs are unable to re-oxygenate the blood sufficiently in ARTERIAL saturation, the adrenal glands will begin releasing EPO to regulate the poor oxygen carrying capacity of the blood. Under normal exercise conditions at common altitudes, only a very small percent of athletes (read "genetic freaks") can desaturate their blood sufficiently to drop arterial saturation levels to the point where an EPO response is triggered. Don't quote me, but I believe this value is just below 90%. At high
altitude, this is much easier to achieve and very often altitude training will trigger an EPO response, especially if a series of short (1:30-3:00 min) high intensity efforts are undertaken specifically for this purpose. Upon return to lower altitudes a well managed athlete will experience an increase in peak VO₂ and performance.

Hope some of this helps.

Alan Carlsson
Engineered Athlete Services