If you are referring to how many pushups to do in one session, the short answer is as many as you can. Aim for a number that challenges you but is still realistic. Build up from day to day to increase muscle strength. If you are referring to how long you should do pushups as a form of exercise, that is up to you. Pushups are a good part of a long-term or permanent exercise regimen. Remember that if you stop doing them, your muscles will weaken.
Under most circumstances, sports drinks do not offer a physiological benefit over water during weight training.[18] However, high-intensity exercise for a continuous duration of at least one hour may require the replenishment of electrolytes which a sports drink may provide.[19] Some may maintain that energy drinks, such as Red Bull that contain caffeine, improve performance in weight training and other physical exercise, but in fact, these energy drinks can cause dehydration, tremors, heat stroke, and heart attack when consumed in excess.[20] 'Sports drinks' that contain simple carbohydrates & water do not cause ill effects, but are most likely unnecessary for the average trainee. More recently, people have been taking pre-workout before working out to increase performance. The main ingredients in these pre-workouts are: beta-alanine, creatine, BCAAs (branched chain amino acids) and caffeine.[21]
Although creatine is a natural component of food, the amount of food required to supersaturate the muscle with PCr may not be feasible. For example, it could require 22 pounds of meat daily [8]. If creatine monohydrate is proven to be a safe and effective ergogenic aid, creatine supplementation may be the simplest way to increasing muscle stores. It may be beneficial to avoid caffeine if taking creatine supplements. One study showed that caffeine diminished strength gains seen with creatine use [9]. 

One limitation of many free weight exercises and exercise machines is that the muscle is working maximally against gravity during only a small portion of the lift. Some exercise-specific machines feature an oval cam (first introduced by Nautilus) which varies the resistance, so that the resistance, and the muscle force required, remains constant throughout the full range of motion of the exercise.
*Always remember: weight loss results & health changes/improvements vary from individual to individual. Just because these studies cite certain data does not mean you will experience these results/outcomes. Always consult with your doctor before making decisions about your health. This is not medical advice – simply well-researched information and tips to sleep better. Thanks for reading!
Collectively the above investigations indicate that creatine supplementation can be an effective strategy to maintain total creatine pool during a rehabilitation period after injury as well as to attenuate muscle damage induced by a prolonged endurance training session. In addition, it seems that creatine can act as an effective antioxidant agent after more intense resistance training sessions.