What you are describing is called Isometric training. It’s a little used, and much misunderstood, form of training in which the muscle tenses without changing its length. Each contraction is typically done for 6 to 10 seconds at a specific angle. For example, think of a bodybuilder holding a front double biceps pose.
During a competition, poses are typically held for quite a long time. That’s why most competitive bodybuilders practice static (isometric) posing. Isometric training assists in holding a pose for a long time without shaking from muscle fatigue.
While isometric training is not popular, it does have its merits as evidenced by a 2005 study titled “Strength training: isometric training at a range of joint angles versus dynamic training” by Folland JP1, Hawker K, Leach B, Little T, Jones DA. That study concluded that:
Isometric training at several equally spaced joint angles can produce
similar full-ROM isokinetic strength gains as full-ROM isokinetic
training. This could be useful for training with minimal equipment or
for designing bodyweight training programs for building strength
through full ranges of motion using only static positions.
Both isometric and isokinetic training do not build strength equally
at all joint angles. Therefore, if your sport or task requires
strength at a specific joint angle, it might be necessary to look at
targeted methods of increasing the strength at that specific angle,
either by partials, eccentrics, isometrics at long or short lengths,
or dynamic exercises that stress a particular ROM.
Isometric training will not provide the mass gains that resistance training will provide. But, it does have some value and should be thought of as an additional tool in your training arsenal.