Answer
The magnitude of $\vec{M}$ is $1196N$ and its direction is to the left.
Work Step by Step
There are 2 forces acting on the arm:
- The horizontal force $M$ that the person's flexor exerts on forearm, pointing to the left.
- The tension in the test apparatus, which reads $T=190N$. It points to the right.
Choose the rotation axis to be at the elbow joint.
- For $M$, the lever arm is $0.054m$.
- For $T$, the lever arm is $0.34m$.
Because the arm is in equilibrium, $$0.054M=0.34T$$ $$M=\frac{0.34T}{0.054}=1196N$$
