Tuesday, January 30, 2018

Literature Review: Moxy vs Portamon sensor

A paper recently came out that addressed differences in the Moxy vs Portamon sensor.  Several interesting points were made as well as some comments.
Firstly, the goals were to see - how they compared to each other in resting muscle O2, exercise muscle O2 measurements, external compression effects, consequences of increased adipose tissue, sensor consistency.

To start with, here is the chart of sensor results at rest:
Note the higher TSI (tissue saturation index) with Moxy in females.  The authors felt this was due to the high subcutaneous fat thickness in females.  Due to the limitations of depth of sensor readings with Moxy, the Portamon apparently was less affected
So the issue of skin thickness appears to affect the Moxy more than the Portamon.

Next was a look at effects of external compression.  This is important as most athletes will use either compressive garments or wrapping bands to keep the sensor in place.   Most compressive clothing will have a pressure less than 20 mmHg, just for general info.  There was a difference in how much compressive force would alter the muscle O2, with Moxy more affected.  So as long as pressure remains constant, the O2 readings should be relatively consistant, but perhaps not on an absolute level.

Test-retest variability: Quite good with both devices, from the paper:

Muscle O2 change with isometric contractions:

There is substantial differences in the degree of O2 desat between devices.  This may be related to probe depth, algorithm calculation differences(Moxy was designed for muscle use only) and/or other factors.  The takeaway in my opinion is that one can't necessarily compare data across different brands of sensors.

Change in O2 with Dynamic arm cranking:
The overall trend was a decline in TSI as the arm cranking power was boosted:

However, individual tracings were very heterogeneous (although Moxy vs Portamon did agree)
The authors did not fully understand why this was so.  One of my criticisms of the use of muscle O2 curves for training, is this ambiguous heterogeneity.

  • Both Moxy and Portamon provide "acceptable" TSI results at rest, during static and dynamic exercise.
  • Moxy may be more affected by fat tissue thickness.
  • Moxy is more affected by external pressure, but if pressure is relatively stable (<20mmHg), the comparative O2 result is valid.
  • Moxy is cheaper than Portamon.
  • From the paper: There have been suggestions as to how
    NIRS might be of use for individual athletes and coaches in, for
    example, tracking and optimizing training. However, in many
    cases, these have merely sought to mimic currently available
    tools, such as lactate thresholds, albeit with the benefit of
    being noninvasive. Even then, differences in optical properties
    of individuals make these measurements unreliable in many
  • Finally, and perhaps most important.  The following was pointed out by the authors:  No one has yet been able to demonstrate a specific benefit
    of using muscle NIRS to track training in an individual.
    What is required is a proper randomized trial comparing the
    use of NIRS to optimize training with current standard methods.