for me functional strength is less about the muscle being able to perform a 'functional movement' optimally or with the most power or even the exercise itself, but more about any muscle group being able to recouperate in a very limited amount of time and being able to repeat the workload regardless of the outside stimulus applied.
thats functional strength. the 'exercises' have nothing to do with it. its how the muscle adapts to stress and its ability to preform the task again and again to the same level of performance as previous demands. thats functional.
