Hot answers tagged progress
I'd recommend doing abdominal rollouts: If you have the space you do them with a barbell (provided the weights can freely rotate), or you can pickup an "ab roller' like the one shown above. They are quite cheap (I picked mine up for ~$5), light and compact. Once kneeling rollouts become too easy, its a matter of progressing to standing rollouts:
There are advantages and disadvantages to both doing more reps/sets and less weights as well as to doing heavier sets and fewer reps. However, in general, I suggest you switch from machines to free weights (http://forum.bodybuilding.com/showthread.php?t=157022873) because of advantages such as including supporting muscles, coordination, flexibility, and so ...
Progression in planks can take the form of added resistance, like you would with other muscles. AKA, add load. Weighted planks. Or weighted reverse planks. http://www.allthingsgym.com/wp-content/uploads/2013/08/Weighted-Reverse-Plank-Chinese-Weightlifting.jpg
The next step is probably dynamic planks. There's a number of them, some of which can be seen here, but the idea is that you're working on maintaining core stability while moving in various directions.
The answer to this question really depends on your goals and available resources, so I'll give a few answers depending on some possible scenarios. Assuming, for some reason, you can only (or only want to) do bodyweight exercises and are stuck indoors: Any/all of the following: Jump squats Pistol squats Burpees Weighted vest (backpack may result in a ...
An excellent squat variation is the goblet squat. This helps build the upper back as well as your legs. Holding a dumbbell or kettlebell in front of you, perform your squats while keeping the implement up. I find it much easier to keep the weight over your center of gravity, which will be your major limitation on using a backpack to weight the squats. ...
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