What factor is most important when evaluating a driver's capability to lift heavy objects?

When assessing a driver's capability to lift heavy objects, upper body strength is particularly crucial. This is because the primary muscles involved in lifting heavy items, such as the shoulders, arms, and upper back, are required to perform lifting tasks effectively. Upper body strength enables the driver to generate the necessary force to lift, pull, or move heavy loads safely.

While other factors such as core strength, leg mobility, and body weight can contribute to overall physical fitness and lifting ability, upper body strength is key when it comes to the specific mechanics of lifting. Core strength supports stability during lifting, leg mobility assists in maneuvering, and body weight can influence overall strength, but these aspects are secondary to the direct role that upper body strength plays in lifting heavy objects effectively and safely.