Costa G, Gaffuri E
Lav Um. 1975 Sep;27(5):129-38.
Borg's RPE method was used by the authors to evaluate physical performance of healthy subjects during exercise tests performed either in the night or daytime and involving different muscle masses (upper and lower limbs). The reliability of RPE scale was confirmed. The perception of physical performance appeared to be higher in the night-time and when upper limbs were involved.