while the murine findings reported by boström et al. appear encouraging, other researchers have questioned whether irisin operates in a similar manner in humans. for example, timmons et al. noted that over 1,000 genes are upregulated by exercise and examined how expression of fndc5 was affected by exercise in ~200 humans. they found that it was upregulated only in highly active elderly humans, casting doubt on the conclusions of boström et al. further discussion of this issue can be found in the wikipedia entry for irisin under the "function" heading.