The following is an example of how to read and interpret muscle oxygenation data. A cycling activity is used in this example, in which the athlete first records his baseline muscle oxygenation (SmO2) at rest (67%) followed by a warmup period starting 1 minute later at an averaged cycling power of 100W, leading to a short spike in SmO2 followed by stabilization at a new SmO2 plateau of 64%.
At the 4-minute mark the athlete engages in an all-out effort at 300W, leading to a sharp drop in SmO2 to a minimum of 46%. The all-out activity is sustained until the 5.5-minute mark, when he engages in active recovery at 50W, allowing his SmO2 to recover to 58%. At 8.5-minutes the athlete goes into complete rest, allowing his circulatory system to catch up with the increased oxygen demand and leading to a peak in muscle oxygenation of 69%.
Note how the SmO2 follows closely the change in power while the heart rate provides us with a delayed and filtered response. This is not surprising, given that the heart must respond to the oxygen-delivery needs of the whole body while SmO2 monitors the balance between oxygen delivery and consumption in real-time, localized within a given muscle.
See the FAQ page What is muscle oxygenation? for more details on SmO2 monitoring and its uses.