Meaning: 'Contract' means to tighten or shorten, referring to the action of muscles during movement.

Wrong options:

• respectively: Respectively is an adverb used to indicate that two or more items correspond to two or more items in the same order, which does not fit as a verb here.
• explored: Explored is the past tense of explore, which does not fit grammatically as it does not describe an action that muscles can perform in this context.
• developing: Developing is a gerund or present participle that does not fit as it does not describe a specific action of muscles in this context.
• pattern: Pattern is a noun that does not fit as it does not describe an action; it refers to a design or arrangement.
• running: Running is a gerund that describes an action but does not fit grammatically as it does not serve as a verb in this context.

Correct answer: running

Explanation: The noun 'running' fits grammatically as it serves as a subject complement following the verb 'produces.' Contextually, it describes one of the types of movement that can be generated by the CPG, aligning with the discussion of muscle actions.

Meaning: 'Running' refers to the action of moving swiftly on foot, which is one of the movements produced by the CPG.

Wrong options:

• pattern: Pattern is a noun that refers to a design or arrangement, which does not fit as it does not describe a type of movement.
• respectively: Respectively is an adverb that indicates correspondence in order, which does not fit as it does not describe a type of movement.
• explored: Explored is the past tense of explore, which does not fit as it does not describe a type of movement.
• developing: Developing is a gerund that does not fit as it does not describe a specific type of movement.

Correct answer: pattern

Explanation: The noun 'pattern' fits grammatically as it serves as the object of the preposition 'of.' Contextually, it refers to the specific arrangement of pulses that dictate the type of movement, which is relevant to the function of the CPG.

Meaning: 'Pattern' refers to a repeated or regular arrangement, in this case, of neural pulses that influence movement.

Wrong options:

• running: Running is a noun that describes a type of movement, but it does not fit as it does not describe the arrangement of pulses.
• respectively: Respectively is an adverb that indicates correspondence in order, which does not fit as it does not describe a type of arrangement.
• explored: Explored is the past tense of explore, which does not fit as it does not relate to the arrangement of pulses.
• developing: Developing is a gerund that does not fit as it does not describe a specific arrangement.

Correct answer: modes

Explanation: The noun 'modes' fits grammatically as it serves as the object of the preposition 'between.' Contextually, it refers to the different states or types of movement that the CPG can switch between, which is relevant to the overall discussion of movement coordination.

Meaning: 'Modes' refers to different ways or methods of doing something, in this case, different types of movement.

Wrong options:

• pattern: Pattern is a noun that refers to a design or arrangement, which does not fit as it does not describe a type of state or method.
• running: Running is a noun that describes a specific type of movement, but it does not fit as it does not describe a state or method of movement.
• respectively: Respectively is an adverb that indicates correspondence in order, which does not fit as it does not describe a type of state or method.
• explored: Explored is the past tense of explore, which does not fit as it does not relate to types of movement.