Final answer:
A loss of lumbopelvic control during exercises such as squats or deadlifts leads to potential lower back strain due to excessive force on the back muscles caused by poor posture and misalignment of the center of gravity.
Step-by-step explanation:
The loss of lumbopelvic control during a squat or deadlift can lead to potential lower back strain. When performing these exercises, good posture is crucial to prevent the exertion of excessive force on the lower back muscles. Figure 9.26 illustrates that with proper alignment, the upper body's center of gravity (cg) is directly above the pivot point in the hips, which minimizes torque and the need for muscle action to maintain balance. Conversely, poor posture, where the upper body's cg is not properly aligned, creates additional torque around the hips that lower back muscles must counteract, leading to increased strain. Squatting or deadlifting with compromised lumbopelvic control can result in large forces that our relatively weak spines are ill-equipped to handle, especially since the back muscles operate at a mechanical disadvantage.