//A class using the child class of the abstract class
public class Rajat {

    //Using the child class of abstract class logic here itself for this example
    public Rajat() {
        //Since Male is a child of HealthAbstract class, the constructor of the Child class is called first and then also the constructor of Health Abstract class is called
        Male m = new Male();
        //Call methods of the Abstract class from its child class
        m.setWeight(70);
        System.debug('The weight is: '+m.getWeight());
        //Call the abstract method of abstract class implemented in child class
        System.debug('Workout Intensity should be: '+m.workoutIntensity(18, 46));
    }
}

//Call the above class in anonymous mode - Rajat obj = new Rajat(); should execute above code