In heavy pulling exercises the bar frequently slips from the hands while the back and legs still have work left. The reason is structural, and it changes how those exercises should be loaded.
The muscles holding the bar are small
Grip comes from forearm flexors whose tendons run through the wrist to the fingers. They are modest in cross-section compared with the muscles of the back and hips.
Force capacity scales with cross-section, so the grip's ceiling is far below what the pulling chain can produce. In a heavy pull the smallest link sets the limit.
This is not a training oversight. The hand evolved for manipulation rather than for suspending a loaded barbell, and its force capacity reflects that. No amount of pulling volume changes the underlying size difference.
Holding is more fatiguing than moving
Grip work is largely isometric. The muscle stays contracted throughout the set rather than alternating between tension and relief as the pulling muscles do.
Sustained contraction restricts blood flow through the muscle, since the pressure inside it exceeds the pressure in the vessels supplying it.
Fuel delivery and waste clearance both slow as a result, so fatigue accumulates faster than in muscles that release tension between repetitions. The forearm works with a restricted supply throughout the set.
Position works against the fingers
The finger flexors cross the wrist, so wrist position changes their available force. As fatigue sets in the wrist tends to extend, lengthening the flexors unfavourably.
A thicker bar increases the moment the fingers must resist, which is why thick-handled implements reduce holding time sharply at the same weight.
Skin, sweat and bar knurling also matter, since much of the holding force depends on friction between the hand and the bar rather than on muscle alone. A worn bar shortens holding time without any change in strength.
The workaround changes what is trained
Straps transfer the load to the wrist, allowing the back and hips to be trained to their own limit. The cost is that grip receives no stimulus in those sets.
Alternating hand positions, using hook grip, or dividing sets so that some are strapped and some are not, keeps both qualities progressing.
Which approach fits depends on whether grip is a training goal in its own right or an obstacle to loading something else.
Grip trains on a different schedule
Because it is small and works isometrically, grip responds to frequent, short exposures better than to occasional heavy ones, and it recovers quickly between them.
Training it with holds at or near maximum load for short durations targets the specific quality that fails in a heavy pull, rather than general forearm endurance. The two qualities improve separately and transfer poorly between each other.
