**Core Concept**
The 'train of four' (TOF) is a clinical technique used to assess the degree of neuromuscular blockade, particularly in the context of non-depolarizing muscle relaxants. It involves the sequential application of four supramaximal electrical stimuli to a peripheral nerve, typically the ulnar nerve at the wrist.

**Why the Correct Answer is Right**
The TOF technique relies on the principle that non-depolarizing muscle relaxants competitively inhibit the action of acetylcholine at the nicotinic receptors on the muscle endplate. By applying a train of four stimuli, the ratio of the fourth (T4) response to the first (T1) response is measured to assess the degree of neuromuscular blockade. A ratio of 0.4 or less indicates significant blockade.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not relevant to the TOF technique, which is specifically used to assess neuromuscular blockade.
**Option B:** The TOF is not typically used to assess the effects of depolarizing muscle relaxants, such as succinylcholine.
**Option C:** The TOF is not a measure of muscle strength or function, but rather a quantitative assessment of neuromuscular transmission.

**Clinical Pearl / High-Yield Fact**
The TOF ratio is an important clinical indicator of the depth of neuromuscular blockade, and a ratio of 0.4 or less is often used to guide the administration of reversal agents, such as neostigmine.

**Correct Answer: D**