Psalms 109:24

My knees are weak through fasting; and my flesh faileth of fatness.

My knees are weak through fasting - not fasting from want of appetite, but the fasting which is practiced by men overwhelmed with severe sufferings (Hengstenberg). (Psalms 35:13; Psalms 69:10.)

And my flesh faileth of fatness - or, 'my flesh deceives from want of oil;' i:e., the absence of the anointing oil makes my flesh unlike what it should be; it is not shining, as in its proper state. So the phrase, Matthew 6:16, "they disfigure their faces" - literally, they make their faces unseen [afanizousi ta prosoopa autoon]; i:e., not shining with oil. The Hebrew [ shemen (H8081)] means oil, not fatness: so in Psalms 109:18. The contrast to "fasting" favours the rendering which refers to non-anointing with "oil" (cf. 2 Samuel 14:2; 2 Samuel 12:20; Matthew 6:16; Micah 6:15) (Hengstenberg). So the Arabic and Ethiopic, the Septuagint, Vulgate, and Syriac. But the Chaldaic supports the English version (Psalms 22:15; Job 16:8).