Is muscle sensations when rowing a boat spindle?

No, muscle sensations when rowing a boat are not spindle. Spindles are stretch receptors that respond to changes in the length of a muscle. They play a role in the stretch reflex, which helps to maintain the body's posture and balance. Rowing a boat involves contracting the muscles of the arms, back, and legs in a coordinated manner. The muscle sensations experienced during rowing are caused by the muscle contractions themselves, not by changes in the length of the muscles.