Thursday, January 13, 2011

The Ultimate Power

I used to think I was cool because I was one of a few that used a power meter on my bike. Those days are gone and it now seems everyone has one. Those who have handed over the coin for one of the various models I'm sure quickly realized the benefits and hopefully improved there training once they understood what the numbers (Watts) were all about. Power is a wonderful thing, especially for an exercise physiologist who is addicted to data. Power is essentially energy measured in Watts so if you are putting out 60 watts you could run a standard 60W light bulb, push a little harder and you could possible run your new LED TV for a while!! Interestingly cycling power output is directly related to oxygen consumption. If you correlate the two during an incremental test you can predict oxygen consumption using power with ~96% accuracy. There is also a linear relationship between power and oxygen consumption. If you know the power you can hold for ~4mins you can predict your VO2max using the equation;

Peak Power Output (4min sustainable power) x 0.01141 + 0.435 = VO2max (L/min)

All you need to do then is multiple the VO2max (L/min) by 1000 to get it into milliliters then divide it by your body mass (kg) and you have a number pretty close to your true VO2max (mL/kg/body mass/minute). This value is probably the value you hear everyone talk about if they have had it tested in the lab. For comparison sake a sedentary individual usually has a value around 30-40. A good age group athlete will be 50-60, the guys/girls winning on the weekends will be 60-70 and an elite athlete will have a VO2max of probably >70. Genetic freaks like Cadel and Lance are up around 90. Although VO2max is a good predictor of performance it is not always correct. There are plenty of athletes that I have tested that score lower than me yet smash me on the road or track!!

OK.. Now back to power. Power is good because it is instantaneous unlike heart rate so when prescribing exercise intensities it is far more accurate and easier to use correctly. Anyone who uses programs like Training Peaks will know their highest held power over increments of time. It calculates it for you then allows you to compare your results with others, this is usually done using Watts/kg.body mass because it makes it all relative. Watts/kg also allows a good picture of possible performance for various athlete types. Absolute Watts is often a good predictor of Time trial performance on a flat course, however once gravity is involved W/kg becomes far more important. A good climber should probably be aiming to be able to hold close to >5.5W/kg body mass going up hill for an extended effort (20-30mins). Some of the data over the years from the Tour de'France has shown Lance in 2004 holding close to 6.97W/kg going up Alp de'Huez on a climb lasting close to 1 hour!! Interestingly for a few presentations Ive done I predicted Lance's VO2max using the equation I mentioned earlier. It went something like this;

If Lance is holding 6.97 watts/kg and he weighs 70kg he averaged 488W. Assuming Lance is holding about 80% of his peak power (which I've chosen from observation) then Lance's Peak 4min Power would have been about 610W. Now.. Using the equation (610x0.01141+0.435) we get a VO2max of 7.39L/min. Multiply that by 1000 and divide by his body mass we get 105mL/kg.body mass. As many possibilities for error this prediction has I try to use it to possibly show a superhuman performance

For a typical cyclist monitoring power data is probably the best and easiest way to track performance over a season or lifetime. Ive been striving now for about 2yrs to get my peak power above 400W. Slowly, (but not yet) i am getting closer to this goal. However, looking at it relatively I hit a mile stone leading up to this years Tour of Bright by finally reaching a  power to weight ratio of a fraction over  6W/kg. Still by no means comparable to the worlds best but good enough to leave most of my riding buddies struggling to hold a wheel when the road goes up.

All in all power is becoming common place in cycling. If you want to brag about how high your power was at the coffee shop after the bunch ride then you've got to do your time at the front because sitting in will save you somewhere in the vicinity of ~30% when compared to the guys pushing the big numbers on the front!!

Tuesday, January 11, 2011

Exercise Nutrient Interactions

Although many of us are aware that certain nutrients are essential for good performance and recovery from exercise it is often overlooked that by manipulating certain dietary components we can alter or even enhance adaptation to training. When we talk about 'nutrients' we are generally referring to the three macronutrients carbohydrate, fat and protein and more importantly how much we need of each to sustain a healthy body and promote adaptation. As endurance athletes we are mainly concerned with carbohydrate (CHO) and to a lesser extent fat (FAT) whereas anyone partaking in resistance training will preach all about protein and its benefits for muscle hypertrophy. In the past sports nutritionists have stressed the importance of a high CHO diet for athletes to be able to maintain high training intensities and also maximize performance. As many of us have experienced when our body becomes depleted of carbohydrate stores intensity suffers and performance declines. This can either be acutely at the end of a long training ride/run or race situation or after longer periods of a restricted CHO diet. As soon as muscle (and more importantly liver) glycogen stores are below optimal everything feels harder. So.... most of us pay attention to these nutrition guidelines and consume high CHO diets to maximize recovery  but also eat bars/gels etc during prolonged exercise to avoid the dreaded 'Bonk' . Ok... Now for some science... If you've read my last post on training adaptation you will have noticed that the body adapts to physiological circumstances that cause cellular stress and sure enough running low on CHO stores is a major physiological stress!! There are a couple of studies that have very clearly shown that training with depleted muscle glycogen (glycogen is a stored form of glucose and glucose is a CHO) can actually magnify the training response. This has been termed as a 'train once daily vs train twice every second day' approach. In these studies subjects either trained once every day so that CHO stores could be replenished after each session (HIGH) or a second group trained twice every second day. This allows the group that trained twice every second day to perform the second exercise bout (usually ~2 hrs after the first) with reduced or low CHO stores (LOW). Both groups over a 3 wk period performed exactly then same amount of training but the LOW group performed 50% of training with reduced muscle glycogen. Amazingly after the 3 wk of training the LOW groups performance in a test of endurance and also several markers of skeletal muscle oxidative capacity were significantly improved compared to the HIGH group. So maybe we can now begin to recommend to athletes to undertake specific training sessions with reduced muscle glycogen and lay off those high CHO recovery meals.

The Molecular Basis of Training Adaptation

It amazes me every time I ask the question to my athletes 'what happens in the body as a result of training that makes you fitter and faster?' No one seems to be able to give me a reasonable answer so I thought I might post a topic that might help explain this deep physiological mystery. Of course there are several components that make up performance but our performance potential is basically limited by our physiological capacity dictated by genetic predisposition. As endurance athletes we are typically limited by skeletal muscle parameters coupled with the cardiovascular system. You may have heard that world class athletes are the way they are because they were lucky enough to have good genes. This is partially true. The human genetic code is basically the same for everyone however some fortunate individuals express specific genes differently. Confused yet? Ill explain... The physiological system of the human body (and any living organism for that matter) is capable of adapting to it's environment. As such when a stimulus is applied (ie, training or running away from a dinosaur) the body does what it can to make sure that next time such a stressful event occurs it is better equipped to deal with it. If you want to understand the big picture you have to think small. Each cell of the body contains the entire genetic code and depending upon the cells role (eg. skeletal muscle, bone or red blood cell) it will express different genes within the genetic code. So each time the cell is stressed certain molecules called transcription factors stimulate certain genes. The primary role of a gene is to encode the sequence to make new proteins and it is the proteins that enhance the cells functional capacity. For example the contractile elements of skeletal muscle are made up of specific proteins that when assembled together form actin and myosin. Actin and myosin have their own specific sequences which is encoded into our genes. When we perform resistance exercise (I'll use this as an example instead of endurance training because its easier to visualize) we stress the muscle cells, activate transcription factors which then stimulate their specific target genes. These genes release the code for the proteins and the cellular machinery can then form these proteins together to form more functional equipment like actin and myosin. So if we repeatedly perform resistance exercise we are continually repeating this cellular process which with time results in more contractile proteins (actin and myosin) and thus bigger muscles. The same goes for endurance training except the proteins made are responsible for using oxygen to break down carbohydrate and fat for energy. So if this process is the same for everyone why haven't I got an Olympic cycling gold medal yet? I train just as hard as those guys! Well.. those guys are lucky because there are other process that display variance between individuals that dictate the upper limits of how much adaption should occur and these are basically set at a higher level for 'genetic freaks'. Without these boundaries we would otherwise from my previous example continually grow muscle and end up as some Hulk like creature with biceps so big we are unable to bend our elbows enough to get food into our own mouths. So.. train regularly to make sure you are continually stimulating new proteins but remember the triggers for these proteins are specific so your training must reflect the way you wish to adapt. Unfortunately there are many inhibiting pathways that regulate why endurance athletes with all of the hours of training they do don't stimulate muscle growth (which would possibly inhibit performance) as well as oxidative capacity. It's called specificity!!!