Q. Shalom Harav, We know one may not tend to there personal needs before davening; is it a violation of this halocho to go on a scale first thing in the morning which takes about 10 seconds. The reason one would choose this time is that the experts recommend going on the scale at this time in order to see the most accurate depiction of ones weight.
A. On question 1019 regarding a man to using a gym and a trainer before shacharis, we wrote; ““Alei Siach (p. 64) writes that Rav Chaim Kanievsky shlit’a answered to a similar question, that it is not correct to do so. Yosef Daas (p.157) mentions different opinions. Tefila Kehilchosa (p. 114, 23) rules in the name of Rav P. Sheinberg zt’l, that if the intention of the individual is to be healthy and strong to be able to serve Hashem better and not for his own benefit and pleasure, it would be considered an act of Heavenly need and is permitted, if it cannot be done at another time. They warn that one should make sure not to miss Tefila Betzibur and the correct time of reading the shema and Tefilah. Hatefilah Vehilchoseha (4: 10) also quotes Divrei Chachamim (1: 2) in the name of Rav Eliyashuv zt’l, that it is permitted since it considered an activity of partial mitzvah. Piskey Teshuvos (89: ) quotes also similar opinions. Horav Shlomo Miller’s Shlit””a opinion follows Horav Chaim Kanievsky Shlit’a only lechatchila.”” See also question1288.
In regard to just weighing oneself on a scale before davening, Horav Shlomo Miller’s Shlit’a opinion is that it is permitted as other personal body needs are, such as taking a shower, brushing teeth etc.
Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit’a