Finding out if an exercise is safe needs to determine the fitness level of the exercise and how much it takes to achieve the result of the exercise. The person performing the exercise needs to know their endurance level and if they are able to perform the exercise without injury or illness.
The first line of defence (or outside defence system) includes physical and chemical barriers that are always ready and prepared to defend the body from infection. These include your skin, tears, mucus, cilia, stomach acid, urine flow, 'friendly' bacteria and white blood cells called neutrophils. Hope this helps.
