Showing posts from 2015

Fractional Utilization, Low Carbohydrate Diets and Running Performance

Fractional utilization refers to the fraction of VO2max that an athlete sustains during an event. It varies between events and between athletes. An athlete can sustain a greater percentage of VO2max for a shorter duration (5000m vs. 10,000m). Fractional utilization is sometimes referred to as lactate threshold. While the concepts are related, they are not the same. Consider an athlete with a VO2max of 70 ml/kg/min: If we find that he can average 90% of VO2max over the course of a 5000m run, he averages 63.0 ml/kg/min for the race. If he averages 86% of VO2max during a 10,000m run, he averages 60.2 ml/kg/min. Athletes may train for years, increasing fractional utilization. By increasing fractional utilization, an athlete will be able to complete a distance at a greater percentage of VO2max. For example, if that same athlete increases his fractional utilization during the 5000m to 93%, he can now average 65.1 ml/kg/min. That 2.1 ml/kg/min increase in utilization means more O2 is cons

So you want to "burn fat?"

Potential for Improving Endurance Performance through Substrate Conservation We know skeletal muscle needs ATP to contract and there are different pathways from which ATP can be synthesized. During endurance exercise, inevitably, some combination of glucose/glycogen and fatty acids will be used for substrate. Utilizing fatty acids for ATP synthesis could be beneficial for endurance athletes because humans have a virtually unlimited supply fatty acids, whereas stored carbohydrate is relatively limited - demonstrated below: 135,000 Cal from stored fat is roughly enough energy for a 65 kg person to run 2000 km (R. Margaria et al, 1963). A decreased reliance on carbohydrate and a subsequent increased reliance on fatty acids during exercise should help to "spare" muscle glycogen. Accepting the well documented theory that low muscle glycogen causes fatigue, one can see how glycogen sparing can potentially extend performance or allow for an acceleration late in a race. &q

Stressors, Ergogenic Aids and Training Loads

Training Basics Training always involves balancing stress and recovery. A stress is applied to the system, the stress results in a deviation from homeostasis, acting as a stimulus for cellular signaling that leads to adaptation. This adaptation will leave the system better able to cope with the stimulus in the future (demand for ATP, substrate transport, muscle recruitment, etc). Generally, there is a dose-response to training so that the more training stress or training load encountered, the greater the signal and response to adapt. For example, if you had two groups of college kids, one group ran 10 miles per week (mpw) and the other group ran 30 mpw - after 10 weeks, the group that ran 30 mpw will likely outperform and/or show greater improvement over the 10 mpw group. Why? Because the 30 mpw group accumulated a greater training load resulting in a greater response. Of course, that's a very simple example. When it comes to training at a higher level - more is not always be

pH Threshold as a Predictor of Endurance Running Performance

Lactate and pH Lactate threshold as a percentage of VO2max has long been associated with distance running and cycling performance. But lactate is not a cause of fatigue. Rather, the accumulation of lactate is an indication of what's occurring. Lactate can accumulate without a change in muscle pH. In fact, lactate production prevents or delays changes in pH. So, could pH threshold be a more sensitive indicator of performance capacity than lactate? Below is data and a graph from a pH threshold test conducted on a treadmill in a lab. From the graph, you can see the lactate threshold falls at roughly 9.5 mph or 6:19/mile. Here, we saw an increase from 3.02 mmol/L to 4.78 mmol/L (+1.76 mmol/L). But note that blood pH did not change from 9.5 to 10 mph (7.38 to 7.37). But, pH did fall between 10 and 10.5 mph. This demonstrates that even though lactate starts accumulating, pH does not necessarily change. In theory, an athlete should be able to maintain a pace in that w