Everybody has an upper limit to what they are capable of as an athlete. That limit is largely set by your parents (Hi Ma!), and the whole point of training is to maximize our genetic potential. What is the latest thinking amongst sport scientists about the determining factors behind endurance performance?
As “gee whiz” as the latest techno gadget is, nothing comes close to matching the complexity and high-tech of the human body. Even centuries after the Renaissance and the invention of calculus by Newton, two events that many consider the start of “modern” science, we are really still in the infancy of understanding the physiology of the body at rest or exercise. Consider that the Wright brothers first flew at Kitty Hawk in 1903, and within 66 years aerospace technology had progressed to landing on the Moon.
In contrast, humans have studied physiology really since the dawn of recorded history, and yet we remain largely powerless against the onslaught of diseases such as Multiple Sclerosis, Parkinsons, Alzheimers, etc. despite the thousands of health scientists and billions spent in research.
Is it then any real surprise that we are also largely in the dark about what, physiologically and psychologically, makes for a champion endurance athlete? There simply is no cut and dried standard template or blueprint for developing athletic potential. Good thing, because it keeps me and lots of other sport scientists and coaches employed!
To celebrate the 2008 Olympic year, the Journal of Physiology published a special issue on sports physiology. This included a review article by major scientists Michael Joyner and Edward Coyle (the latter, you may recall, tracked Lance’s physiological evolution through the 1990s) on the determinants of a champion’s physiology. Let’s take a peek…
Cycling and Running Models
The bulk of modeling human performance has primarily used data from cycling and especially running. The latter has been especially dominant in sport science literature because of the long history of data such as world records. Running events also take place under generally standardized conditions, unlike cycling races apart from track events. Many running and cycling athletes have also been fairly regularly tested or monitored over their careers. Another factor is that treadmills and cycle ergometers were amongst the first laboratory simulators to be developed, permitting a good record of correlation between lab-based research and field data.
Overall, at the broadest level, the three primary determinants for performance appear to be aerobic capacity (VO2max), lactate threshold, and also the newer concept of “efficiency.” As we will see, each of these factors are important separately, but interact with each other also.
VO2max As most of us know, VO2max stands for our maximal oxygen consumption, and had long been considered the be-all and end-all of endurance performance. For example, it has been measured since the 1930s in champion runners. Typically expressed either in absolute terms (e.g. 4.5 L/min) or normalized based on body weight (e.g. 65 mL/kg/min), this value denotes the amount of oxygen being utilized by your body. Therefore, it is an indicator of the aerobic capacity of your body, and forms the “ceiling” of your endurance performance. Champion male endurance athletes typically have values in the range of 70-85 mL/kg/min, 50-100% higher than in “normal” subjects. Note that max values will differ between sports, based on the amount of muscle mass employed (e.g. highest tends to be with cross-country skiing) and also sport-specific factors (swimmers tend to have lower values due to buoyancy effects).
VO2max represents an integrative value comprised of many physiological factors including:
• The ability of your heart to receive and pump out large volumes of blood (cardiac output). This comes mainly down to stroke volume, or the amount of blood pumped per beat of the heart.
• The amount of hemoglobin in your body (think altitude training or illicit blood manipulations)
• The efficiency of your blood delivery to your muscles (it’s no use carrying lots of oxygen if it gets frittered away from the active muscles).
• The ability of your muscles to extract oxygen from the blood (training also improves your cell’s ability to both extract and use oxygen).
• The ability of your respiratory system to deliver sufficient oxygen to the lungs to transfer to the blood.
While it is obvious that, at the elite levels, a certain VO2max is the basic entry requirement for world-beating performances, it also quickly became evident that endurance performance beyond 10 min or so is conducted at intensities less than VO2max. Put another way, your power output for a 20 km TT is much lower than what you would crank out during a VO2max test. For example, a marathon pace is typically 75-85% VO2max, a 10 km run pace is 90-100% VO2max, and a 5 km run close to 100% VO2max.
So if you can’t predict peak performances with just VO2max results, what else can you use?
Lactate Threshold (LT)
LT or Performance VO2max is the second important parameter. This is the wattage you can sustain without a significant accumulation of lactate (the primary end-product of anaerobic metabolism and what generally makes your legs burn with high exertion) in your muscles and blood. In turn, this is widely variable within an individual depending on training state, and also across individuals depending on numerous factors.
Out on the road, estimating the LT is the purpose of many field tests that are employed by coaches, which generally are variations of a 10-25 min TT effort.
Many of the determining factors are identical to those determining VO2max, but another important factor becomes the ability to buffer or dissipate lactate. Remember that lactate is a dynamic function of both production AND removal from the muscles, and you can improve your lactate threshold by improving either side of the equation.
LT intimately interacts with VO2max, and a simple example illustrates this relationship and the importance of LT:
• Rider A has a VO2max of 60 mL/kg/min, but his LT is at 70% or at 42 mL/kg/min.
• Rider B has a VO2max of 50 mL/kg/min, but his LT is at 90% or 45 mL/kg/min.
All else being equal, Rider B may have a lower ceiling, but is able to work at a higher relative percentage, with an end result that he can ride at a harder intensity.
What may not be equal, even if the two riders are identical in height and weight, is the third factor:
Efficiency
This is really an umbrella term for a very wide range of factors, but ultimately, they all revolve around the oxygen costs required to ride at a set wattage. The lower the energy costs to ride at 200 W, for example, the less overall metabolic demand for a finite (energy) resource. This is analogous to the idea of financial “return on investment.” Why spend $150 to make $200 when you can invest smarter and spend only $100?
In the previous example with LT, Rider A can counter Rider B two ways physiologically:
1. Train his LT to get it to a higher percentage of VO2max. Even if he can get it to 80% (60 x 0.8 = 48 mL/kg/min), he’ll have the advantage.
2. Really work on his efficiency, so that he can ride the same wattage using 42 mL/kg/min as Rider B can at 45 mL/kg/min.
Some of the vast number of factors determining efficiency includes things that we have previously covered in great detail on Toolbox, including bike fit and pedaling dynamics, so it absolutely does pay off to place emphasis on the technical aspects of bike riding. Adding to that are larger issues with strategy and tactics, such as drafting and pack positioning.
Summary
Peak performance is a synergy of multiple physiological, biomechanical, and tactical mechanisms. All of them require attention from both athletes and scientists, and I’ll devote my next article to exploring some of the new frontiers and unanswered questions in this field.
Speaking of elite athletes, I’m currently reading the autobiography of climbing legend Ed Viesturs, who has climbed all 14 peaks in the world >8000 m peaks, all without supplemental oxygen (plus living to tell the tale!). The title, No Shortcut to the Top is perfectly appropriate to him and also to training for your own peak performance! Keep it tuned to Pez Toolbox in 2008 and ride strong!
Reference
Joyner, MJ and EF Coyle. Endurance exercise performance: the physiology of champions. Journal of Physiology 586:35-44, 2008.
About Stephen:
Stephen Cheung is a Canada Research Chair at Brock University, with a research specialization in the effects of thermal stress on human physiology and performance. He can be reached for comments at thermal.doc@gmail.com
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