Final answer:
Lactate and H+ (decrease in muscle pH) affect the actomyosin complex by triggering muscle contraction and causing muscle stiffness and fatigue.
Step-by-step explanation:
Lactate and H+ (decrease in muscle pH) have an effect on the actomyosin complex. When lactate is produced during anaerobic glycolysis, the internal pH of the muscle can decrease. This decrease in pH can trigger contraction in the muscle due to the activation of motor neurons. Additionally, the acidic conditions caused by lactate accumulation can inhibit the left-to-right reaction of the actomyosin complex, leading to muscle stiffness and fatigue.