@TomKindlon Thanks for sharing this article, Tom. Our @4WorkWell group proposed a heart rate formula in 2010 that was evaluated in the study. The threshold was intended to help people with #MECFS avoid exceeding their heart rate at ventilatory anaerobic threshold. pubmed.ncbi.nlm.nih.gov/20185614/
@TomKindlon @4WorkWell I think it’s important to point out the equation we proposed was never intended to accurately predict heart rate at VAT. It was intended to slightly under-estimate heart rate at ventilatory anaerobic threshold. The thought was this underestimation would provide a safety margin.
@TomKindlon @4WorkWell The authors of the present study, very helpfully, provide us with some important subject-level data in Figure 1. These data can help us get an idea of whether the formula we proposed in 2010 actually underestimates the heart rate at lactic acid threshold, as originally intended.
@TomKindlon @4WorkWell In Figure 1, calculated thresholds using the equation we proposed on the left. Actual threshold obtained during CPET on the right. Lines connecting the dots indicate calculated and observed data came from the same subject. Data for men and women are present in separate plots.
@TomKindlon @4WorkWell So, let’s take a look at the results for women (below). The distribution for calculated heart rate (left) is clustered below the observed heart rates (right). This observation supports that the 55% formula underestimates actual LAT measurements in general, as intended. 
@TomKindlon @4WorkWell Now let’s look at each case. In general, lines for each individual subject slope upward from left to right, meaning that the trend we see at the group level is also common at the individual level. This is good to know, because clinicians work with patients on an individual basis.
@TomKindlon @4WorkWell Now let’s look at the men. Here, we see the same trends as the women: (1) calculated group distribution is, on average, lower than the distribution of actual CPET measurements, and (2) most of the calculated values were less than the observed values for each individual subject.
@TomKindlon @4WorkWell The big concern for me as a physical therapist is that we would overestimate the heart rate at VAT/LAT, because the pacing program would include activities that are too vigorous for a patient. So next, I tried to count the number of subjects who might have had an overestimate.
@TomKindlon @4WorkWell According to Figure 1, the 55% equation would overestimate heart rate at VAT/LAT in 14% of patients. This means to me the equation was correct on underestimating the heart rate 86% of the time. For context, in rehab practice, this is a well-performing test; a good place to start.
@TomKindlon @4WorkWell (Of course the major limitations to the analysis described in the previous tweet are poor screen resolution and my failing near vision. 😅)
@TomKindlon @4WorkWell So, why does this matter? Perhaps it’s best summarized as: “All models are wrong. Some models are useful.” Formula based estimation for metabolic output using heart rate is fraught. We know there are additional problems with it from our work on chronotropic intolerance in #MECFS.
@TomKindlon @4WorkWell However, because (repeat) CPET measurements is still not a common evaluative assessment for people with #MECFS, patients and their physical therapists are left with few objective tools to monitor activity in our collective attempt to reduce post-exertional neuroimmune exhaustion.
@TomKindlon @4WorkWell Calculated values, for all their acknowledged problems with picking accurate values in single patients, still can be useful to help patients and clinicians select appropriate activity thresholds for pacing self management. The data from this study seems to support this premise.
@TomKindlon @4WorkWell We are early in the process of putting together a webinar on pacing considerations for #MECFS, including the practices and pitfalls of using heart rate as an objective criterion. Time and date TBA. 😊
