Final answer:
The term referring to excessive frequency of training leading to decreased performance due to inadequate rest and recovery is overtraining. This can cause injuries and is distinguished from overuse, overreaching, and supercompensation.
Step-by-step explanation:
The term that refers to excessive frequency, volume, or intensity of training resulting in a reduction of performance, which is also caused by a lack of proper rest and recovery is C. overtraining. This condition arises when the physical demands placed on the body exceed its ability to recover, leading to decreased performance, and could potentially lead to injuries such as damage to the muscle fibers, tendons, and even bones. In contrast, overuse typically refers to repetitive stress injuries, overreaching is a short-term version of overtraining which is recoverable in the short term, and supercompensation refers to a phase where the body rebuilds itself stronger after training and recovery.