In order to strengthen your arm muscles it is recommended that you do exercises with weights. If you do not have weights you can alternatively use two filled 1-liter water bottles. Take one weight in each hand and get into the starting position where you have your feet shoulder-width apart. Tighten your entire body and stretch your straight arms until the horizontal plane and then back towards your body. Complete this exercise 20 times and repeat it after a short break of 15 seconds.