PS

*mV(ˀ)n(-at)- - tendon, sinew; muscle (SED I No. 183)

Cf. *matn-  (1) ‘sinew, tendon, nerve’ (No. 191), related with metathesis?

Akkadian
manānu - sinews (CAD m1 208)

(pl.t.). To be analyzed as man­-ān-­, with ­-ān- as a plural suffix. In most contexts, however, can be equally treated as manān­-ū/ī, with a common masc. pl. suff. ­ū/ī. 

Syriac
mentā - crinis; nervus; chorda; tonus (LSyr. 393)

Vestiges of ­-ˀ- in Syr. rather point to *-ˀ-­ in the protoform; otherwise a biconsonantal root, with doubling of -n- (and probably with insertion of ­-ˀ as a second radical). 

Arabic
maˀnat- - the entire part of the belly that surrounds the navel (BK 2 1054)

Vestiges of ­-ˀ- in Arb. rather point to *-ˀ-­ in the protoform; otherwise a biconsonantal root, with insertion of ­ ­-ˀ as a second radical in Arb. What is meant is probably rectus abdominis, a straight muscle of the abdomen.

Tigrinya
mnat - arm muscle (Bass. 103)

Probably, *-ˀ-­ in the protoform; otherwise a biconsonantal root, with triconsonantizing strategy, namely inclusion of the ­-at-­ suffix into the root as a third radical.