Back Squat Safety Considerations

Learning how to keep a locked straight back is extremely important when bearing heavy loads (squat, dead lift etc). If you find your back to be sore, you are most likely allowing unsafe curvature of the spine which results in excessive lumbar strain. Chrissy explains in the following video a few common techniques to learn how to properly hold your back in place (she talks about the dead lift but it applies for the squat as well, only the beginning really applies):

Learning to keep a straight back and developing proper hip, glute, and hamstring flexibility is extremely important to correctly and safely squatting. Proper general strength, form, and fitness for more explosive movements.
I recommend a faster and more explosive concentric or upward movement in the squat. If your form is improper or you try to do too much weight too soon, you risk improper strain on your back. I recommend staying at a slow pace until you master form, and have good general strength to engage in higher velocity movements. This video is great for learning proper form, and avoiding squatting mistakes:

How much weight should you use? 85% of your 1 rep max, meaning 85% of the weight you are able to do once is a great way to maximize strength and muscle fiber recruitment. Movement focus The downward portion should be under control and take about 4 seconds. There are other “ballistic” versions that are done with a very quick eccentric phase, but this is about building general strength. The concentric movement should be done as quickly as possible. Aim for a 2 second upward movement. The importance is the “intent to move explosively” in order to get the most transfer to the actual movement of the vertical jump. 
Frequency. How often should you squat? Although this can vary for each individual, because each individual has a different ability to recovery from stress, and super compensation from the body may be further developed in some than others, if you are trying to attain maximum strength it is advised to squat twice every 8 days with at least 48 – 72 hours of recovery. IF you go into the weight room, and the same weight feels heavier than before you have not allowed sufficient recovery time and are risking potential injury. IF you are feeling sluggish, tired etc.. consider taking more days off. One of the leading risks of injury AND lack of results is over training. Consistent and satisfying results can be obtained by providing that extra day of rest to your training. Reps and Sets and resting time. The number of reps is much more important than the number of sets. You want to work with the heaviest amount of weight, with the highest speed possible. You do not want to lift fatigued or slow. If you are having to pause the load or “getting stuck” lower the weight or lower the amount of reps per set. Try to accomplish 3 – 6 reps with 85% of your 1RM. Aim for a total of about 25 reps with this load. Remember sets are just there for convenience, if a set slows, stop it, recover, and start again. Give yourself enough rest in between sets to give your absolute max effort to each set. This may even take up to 2 – 5 minutes. You are not training your endurance, you are training your power. Don’t go for the burn. The goal is to move heavy weight at high speeds. Warming up Activity specific warm up is extremely important. A general dynamic warm up followed by a couple sets with 25 – 40 % of your 1RM, will allow your muscles to warm up to a specific activity and prepare for higher loads and greater stress. Concluding pointers 1. Make sure you are working your glutes and not just your quads. Lift your bottom through the movement, and feel your glutes activate as you drive your hips through. Activating your glutes, and building strength in these fast twitch muscles will help you better use you glutes during the actual jump. Stick your bum out there… 2. Box squats that allow you to touch (not completely sit) a point and explode back up are a fine training tool. Do not completely sit on the box and allow the weight to compress on your back. find a box or bench that represents a parallel position of the legs. 3. In general you want to achieve 2.5X your body weight in the squat. You need to build enough strength that your speed is not slowed by the resistance of your body. If your squat is low, your entire body is heavier to your legs, and your contraction speed will be slowed, and your jump lower. Before you can think about an absolute max contraction speed, you have to achieve the requisite strength to overcome the resistance of your body weight. 4. Carry over to the vertical jump, and maintaining current speed level. The suggestions in the jump manual for accommodating exercises, synaptic facilitation, contrast training, overs peed training, and plyometrics will help you maintain and increase current abilities even while your focus is on strength. Please refer to The Jump Manual to make sure you are incorporating these methods. Other recommended Resources: Take it all in, and perfect your form. It will pay off long term:

For the Complete Program To Jump Higher For Your Specific Situation,
Click Here On The Jump Manual