We read with great interest the recent study by Franchi et al which concluded that changes in muscle thickness measured via ultrasound tracked well with changes in anatomical cross‐sectional area measured via magnetic resonance imaging (MRI). While this is a very important study due to the widespread use of ultrasound in training studies, there may be a slightly more advantageous way to analyze the results. A correlation between the percentage change in muscle thickness and the percentage change in anatomical cross‐sectional area was computed, yielding a significant correlation (r = .69). This correlation appeared to be primarily driven by four limbs (likely from two individuals) detailing a major limitation with correlational analyses as they can be skewed by outliers and are reliant on sufficient variability in the data. We used a graph digitizer to estimate the values provided in the figure (Figure 4A of Franchi et al) and computed the exact same correlation (r = .69), which was negated when excluding the four limbs that responded to a much greater extent than the rest (r = .34; P = .236).An alternative analysis exists through equivalency testing to assess whether the two measurements were not too different from one another. While a traditional t test examines whether a 95% confidence
Scandinavian Journal of Medicine & Science in Sports – Wiley
Published: Jan 1, 2018
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