This is the question once a while every fitness freak ask or once a while this question has been crossed there mind which is better cables or dumbbells for gains. This is the valid question and it seems like it has troubled you tools like me. To understand the valid reason to justify which is better we must need to know about the pathway of exercise in weight training.
In weight training, there are only two types of pathways (the trajectory of movement of weights during repetitions) are present which are:-
1. Linear pathway
2. circular pathway
The linear pathway is also called a straight pathway. The linear pathway are those in which the weight travel in a straight line. Like in bench press the weight moves in a straight line, this line is always perpendicular to the ground. All the compound movements work in linear pathways i.e bench press, squat, deadlift, shoulder press, etc. For maximum muscle development, we have to always do compound movements with free weights using a dumbbell or barbell. Compound movements or exercises are those which involves more than one muscle group and there is more than one joint involve during movement i.e deadlift as while doing a deadlift the muscle of our entire posterior chain get involved including our back muscles, glutes, hamstring, in a deadlift our hip joint, knee joint, shoulder joints get involved thus making it as a compound exercise.
We have to do all compound exercises with free weights (dumbbells or barbell) because we have to create a linear or straight pathway in order to do these exercises correctly and in order to create the linear pathway our muscles involvement, muscles engagement increases and simultaneously our stability increases. And in the long run, this leads to better lifting form, technique and a good posture which ultimately helps in gaining confidence to lift heavy weights. Thus when you start lifting heavy weights in compound exercises you start building more quality muscles mass eventually along with a positive hormonal shift in favour of physique development.
In the circular pathway, the weight moves in curvature, the trajectory of the pathway is circular. The weight travels in the form of an arc of a circle i.e during biceps dumbbell curl our weight travels in a circular path between start point to an end point of an exercise. To get maximum benefits in exercises which have circular pathways we have to perform all the circular movements with the help of a cable this is because of the two reasons which are:-
1. Cable provides a continues tension.
The continuous tension refers to the fact the resistance supplied to the muscles during a cable exercise is uniform throughout, while doing exercise with dumbbells the tension does not remain uniform throughout. For example, during a biceps dumbbell curl, the most resistance is experienced when there is a ninety-degree angle at the elbow joint. Here our biceps resisting against 100% of the resistance force (i.e. the gravitational pull of the dumbbell towards the ground). As we curl more the resistance is reduced, with the resistive force lowered by roughly 30% when the biceps reaches forty-five degrees. The continuous tension provided by a cable is due to the pulley system which lifts and lowers a weight stack, and the weight stack is always moving in a straight line, thus it always experiences the equivalent resistive force throughout the movement. Thus due to the continues tension, our working muscles get uniform load throughout the movement which makes it more suitable for all circular pathways exercises.
Secondly due to the pulley system which also allows the line of resistance to be dynamic. The dynamic line of resistance means that we get constant progress, a constant change throughout the movement which helps our muscle to move in a full range of motion. As in free weight, there is a restricted movement between a start point and end point of exercises when you do it scientifically but in the case of cable this restriction get subsides due to the dynamic line of action of cable thus we can move our muscles in full range of motion.
So perform all your isolation exercise (which targets specifically only one muscle group and there is only one joint involve during movement of the exercise) i.e biceps dumbbell curl, in bicep dumbbell curl mainly biceps brachii muscle is primarily targeted and only one joint the elbow joint is involved, thus it is an isolation exercise. To get maximum muscle engagement, and better muscles mass growth it is best to do all isolation exercises with cable.
Bottom line is that do all compound exercises with free weights (dumbbell & barbell) and do all isolation exercises with cables for maximum gain in muscle size. In last I would like to suggest you that use these tips to maximize your muscles gain and build better physique by utilizing all the time spent inside the gym. All the best.