Final answer:
To help a client exhibiting excessive extension of the lumbar spine during a multiplanar lunge to balance exercise, they should be instructed to engage their core muscles and maintain a neutral spine. Limiting range of motion and performing modifications can also be beneficial.
Step-by-step explanation:
Excessive extension of the lumbar spine during a multiplanar lunge to balance exercise can be corrected by providing the client with proper instructions. The client should be instructed to engage their core muscles and focus on maintaining a neutral spine throughout the exercise. They should also be advised to limit the range of motion to a comfortable and controlled level, avoiding any excessive arching of the lower back. Additionally, the client can be guided to perform modifications or regressions of the exercise that reduce the demand on the lumbar spine, such as performing lunges with a shorter step or using support.