A Smarter Way to Train
Whether you decided to run your first 5K race or participate in your 10th Ironman 70.3, all training begins with a workout plan. But which plan should you use? Among the thousands out there, most are based on distance, pace, time, and/or heart rate. They are well-established and commonly used — especially those based on heart rate. However, they’re not without their flaws…
Training plans with heart rate generally require athletes to determine their maximum HR, and then incorporate the use of HR zones (as a % of max HR) that athletes should be in when performing their exercises. HR is used to indicate and track the intensity of the workout. However, many plans require athletes to subject themselves to 30 or 60 minute time-trials where they run or cycle as fast as they can for that period of time on a regular basis in order to determine their Lactate Threshold Heart Rate (LTHR).
Not only are time trials extremely stressful on the body, there are two inherent issues with relying strictly on HR to guide workouts:
- HR is a moving target:
Not only will it change at the same workout intensity as you get more or less fit, but it’s also affected by a number of external factors, such as differences in your day-to-day stress levels, caffeine intake, and prior rest.
Even more difficult to control is cardiovascular drift, which refers to the increase in heart rate that occurs when running at a consistent pace with no increase in effort. This is caused by an increase in your core body temperature, leading to a decrease in stroke volume (the amount of blood your heart pumps with each beat) and corresponding increase in heart rate (in order to keep the same amount of blood flowing through your body). Many endurance athletes mistakenly believe that if they run or cycle at a steady pace, their heart rate will remain constant. On the contrary, heart rate can vary by as much as 20 bpm!
As a result, you could be training in the correct HR zone but giving the incorrect amount of effort that the workout is calling for. Or, vice versa, your HR might indicate that you are in the wrong zone when you are actually putting forth an appropriate amount of effort.
2. HR is used as a proxy for your lactate threshold:
First off, what is Lactate Threshold? It is the exercise intensity at which lactic acid is building up in your muscles faster than your body can clear it and begins to ‘build up’ in your blood. In running or cycling terms, it’s commonly measured as the max pace that you can sustain for about 60 minutes (related to functional threshold power). Check out Joe Friel’s detailed explanation of lactate threshold and exercise intensity for more info.
Regardless of whether you believe that lactic acid causes muscle fatigue or not, its buildup is correlated with the amount of oxygen available in the muscle and fatigue, which is why lactate threshold is so important to endurance athletes.
Until recently, the athletes had only two ways of determining workout intensity in real-time: by feel or by HR.
The issue with training by feel is that most athletes don’t know how hard to push themselves in order to optimize performance. Compare the mile splits at the Boston marathon for amateur runners vs the winners. The amateur runner gradually gets slower and slower as the race goes on, while the winners keep practically the same pace the entire race.
The issue with using heart rate goes back to an earlier point — it is affected by so many external factors, let alone the improvements you’re making over time, that it can’t be considered reliable to get you training in the right zones.
Instead, a more effective method to measure workout intensity is by also monitoring your muscle oxygenation levels.
Before we dive in, let’s make sure that we’re all on the same page as to why muscle oxygenation is important to endurance athletes.
Muscle oxygenation (SmO2 %) is a measure of the oxygen content in the tissue (muscle) of your body that is being monitored.
Cellular respiration is one of three processes by which your muscles use oxygen to produce energy. Endurance athletes rely on the delivery of oxygen (via the aerobic system) to power their muscles — in fact, the aerobic system contributes about 70% of the energy required to meet the physical demands of endurance sports. Consequently, understanding how muscles utilize oxygen is critical to developing a training plan that improves running, cycling, and swimming performance.
Further, the human body’s lactate threshold is the point at which lactic acid rapidly accumulates in your muscles. Lactic acid is produced as a result of a deficit of oxygen in the muscle and thus there is a strong inverse relationship between the lactic acid and muscle oxygenation levels during exercise.
So why is SmO2 % an effective measure for endurance sports training?
1. It allows you to monitor individual muscles rather than overall exertion by the entire body.
Clearly not all exercises require the use of the same muscles. Certain muscles may be more or less developed in any athlete and different types of exercise affect them in different ways. It’s imperative to be able to measure how each individual muscle is working to get an accurate view of the amount of effort exerted and the level of fatigue.
2. It contextualizes your workouts by providing dynamic measures of maximum output capacity.
When a workout calls to run at 60% of your max heart rate or max power, it really intends for you to put forth 60% of your max effort level. The reason why HR or power is inadequate as an absolute measure of workout intensity is that not only are they reliant on external factors, but your max output capacity is different from day to day. It depends on how much you exercised in previous days, how much you slept, how your nutrition has been, etc. etc. Workout plans based on HR or power place static markers on a dynamically moving target. Only SmO2 can accurately let endurance athletes know if they are truly are putting forth 60% of the max effort level at that given moment.
That’s not to say that you should stop using these measures all together. When used in conjunction with SmO2, the data captured by HR and power meters can be extremely valuable. By understanding the underlying concepts behind all of these devices, you will be able to reconcile the external and internal load your muscles experience, leading to a greater understanding of your body and an improvement in performance.
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