Near-infrared spectroscopy (NIRS) is a powerful non-invasive tool that allows researchers to measure, in real-time, the changes in oxygen dynamics in a myriad of tissues during a variety of interventions from sitting to exercising. One of them most useful functions of NIRS is its utility in measuring skeletal muscle oxidative capacity. This technique has even been validated against phosphorus magnetic resonance spectroscopy (P-MRS) and high resolution respirometry (HRR) which are considered the gold-standard measurements for mitochondrial function. In both of the above studies the NIRS technique, described in detail below, was shown to be significantly correlated to each gold-standard measure (r > .88, p < 0.0001) and (r = 0.61 – 0.74, p < 0.01), respectively. Very briefly, to measure skeletal muscle oxidative capacity, a seated participant contracts their muscle (to provide a metabolic stimulus), then undergoes a series of 5-15 rapid cuff inflations, from a blood pressure cuff located proximal to the area of interrogation. Upon completion the cuff/s are inflated above systolic blood pressure for 3-5 minutes in order to normalize the NIRS signal. Finally, the slope of each cuff is measured, plotted, and fit to a monoexponential curve allowing for the determination of the NIRS rate constant, k, which is the value used as a surrogate for skeletal muscle oxidative capacity.
NIRS in Research. Near-infrared spectroscopy (NIRS) is a relatively new technology that has shown utility for many different non-invasive protocols for physiologic experimentation. Essentially, NIRS technology monitors changes in capillary oxygenation values by measuring the intensity of light (600-1000nm) after it passes through biological tissue, (i.e. skeletal muscle). The amount of light that is absorbed by a tissue depends mainly on the amount of oxygen that is bound to the chromophores, hemoglobin and myoglobin, underneath the sensor. Therefore, by measuring dynamic changes in the amount of light that passes through a tissue, researchers are able to get an idea of oxygen consumption within the tissue underneath the sensor.
While science does a great job of measuring the statistical norms of a population, the individual physiologic response to training must be taken into account in order to maximize an athlete’s performance potential. Training autoregulation is the concept that training should be monitored and manipulated on a daily basis, based on the individual physiologic responses of the athlete. In the last blog post I introduced the concept of autoregulation and how monitoring skeletal muscle oxygenation levels via NIRS could provide useful insights to how an athlete is coping with a workout. In the next couple of posts I want to walk through the analysis/real-time monitoring of an athlete completing a repeated sprint style workout, and a lunge based body weight strength circuit.
Scientists and coaches have long been searching for the perfect interval workout that pushes the athlete hard enough to elicit a specific adaptation while keeping them healthy enough to continue to train consistently. Such studies have resulted in the creation of guidelines for set and rep schemes for both strength and endurance training aimed at targeting specific adaptations. While this research has gleaned many generalizable rules, these rules have a tendency to fall apart when applied purely on an individual basis. Even something as simple as hypertrophy training (3-5 sets of 8-12 reps) does not always elicit the mass gain it promises. Speaking from experience, it’s extremely frustrating to complete prescribed workouts, with what seems like adequate stimulus, without gaining the benefits that are touted.
Over the last few blog posts, I have outlined how to Complete and Analyze a 5-1-5 Assessment. Briefly, a 5-1-5 assessment consists of progressively harder load steps where 5 minutes of work are followed by 1 minute of complete rest, then repeated. After the load is repeated twice it is increased until the athlete cannot finish a load or has completed sufficient work to gain enough information about their physiology. Using this data one of three major physiological limiters can be identified.
The last blog post discussed how to complete a 5-1-5 Assessment to evaluate which system: cardiac, pulmonary, or muscle oxidative capacity was most limiting to an athlete’s performance. In this post I will detail how to interpret the data to determine which system is most limiting. Upon completion of a 5-1-5 assessment, 2-3 graphs will need to be analyzed. 1) A total hemoglobin (THb) response graph which indicates how much blood is present underneath the sensor and 2) A muscle oxygen saturation (SmO2) response graph which indicates how much hemoglobin is oxygenated in the capillaries under the sensor. Optional: a third graph with heart rate response. Its typically more helpful to have the power/speed step graph overlaid with each graph to know when the power/speed is changing. Limitations are typically identified by trends in the THb and SmO2 response curves rather than by looking purely at the number values presented from the data. These trends help to identify the underlying physiology which then sheds light on the limitations being experienced during this assessment.
Purpose:The purpose of most physiologic testing is to find maximal or threshold values in order to better predict or dictate an athlete’s potential for performance. However, things like VO2max, the maximal amount of oxygen an athlete can uptake and utilize, is only predictive of performance across wide ranges of athlete prowess (Levine 2008). Determining threshold values, the point at which global-body homeostasis can no longer be maintained, may lend more credence to predicting an athlete’s performance (Heuberger et al. 2018) but in terms of dictating training, it is only a starting point. Determining threshold values allows for the simplification of training by creating training zones. However, it does not describe how the body is being limited during exercise. Endurance performance is primarily aerobic, therefore any process in which oxygen is up taken, transported, delivered, or consumed can be limiting to an athlete’s performance. There are three major systems that assist in aerobic metabolism, the pulmonary, cardiovascular, and skeletal muscle. Because of the inherent limitations with current testing protocols, the 5-1-5 Assessment was created. This assessment was designed to identify the greatest limiter (lungs, heart, or muscle) of an athlete’s physiology.
In the last few blog posts I identified a significant right left quad oxygenation imbalance during both cycling and stair climbing. In order to legitimately test the extent of these imbalances, I recently completed a standard 4-1-4 assessment using my stationary cycling power meter. Briefly, a 4-1-4 assessment consists of one load (i.e. 200W) of 4 minutes on/1 minute off/4 minutes on, then the load is increased. This pattern is repeated until the athlete cannot finish one of the 4 minute sub-stages.
In the last blog post I detailed discrepancies in desaturation patterns in the right and left vastus lateralis during a mountain biking workout. In this workout I saw a slowed warm-up response in the left leg. Further in the workout the right leg wasn’t desaturating as much as the left. In order to further test if these discrepancies exhibited, are sport specific, I wore Moxy’s on both VL’s, again, and did an interval workout on the stair climber.
Injuries are one of the major causes of stagnation or lack of progress during training. I am sure many of you have been there, you are working very hard towards your next big goal race, then, during one of your major training sessions you feel the start of a dull ache in the front of your knee. Your first thought is “Oh it’s nothing, just a little soreness from all the hard work I have been putting in.” The next day you can barely walk without shooting pain from your knee to your hip. You take a day off, rest, ice, and foam roll, and next thing you know it’s been three weeks of no concerted training. The next time you complete a solid training session you feel as if you lost ALL of your progress. Any athlete who has trained for an extended period of time has experienced the pain and disappointment of an overuse injury. For those of you who have experienced this the main recommendation from most coaches, trainers, or doctors, is to get more rest and don’t push yourself as hard. Essentially, you need to recover harder and smarter. While I believe that proper rest and recovery is EXTREMELY important to longevity in any athletic pursuit, I don’t think it’s the only piece of the puzzle, especially if you continually get injuries only occurring on one side of the body. The prediction of an overuse injury is almost impossible and it’s extremely challenging to identify how or why these types of injuries occur. While I have written a lot about using Moxy to dictate training I want to start to explore how Moxy could be used to identify unilateral differences in muscle oxygenation, and how this could be used to prevent or potentially identify weaknesses that could cause overuse injuries.