A lot of what your brother is telling you is correct. There have been several studies conducted on teen weight lifting that suggest that certain types of weight lifting may damage the epiphysis, or growth plate, of your bones. There is evidence that lifting heavy weight could speed up growth plate closure, which would stunt your growth.
That does not mean that you should not pump iron, you just want to avoid power lifting, competitive lifting and maximum lifts. You should use relatively lightweights and do 2-3 sets of no more than 15 repetitions. You should also try to limit your workouts to 3, half-hour sessions per week.
It is important to learn the basics of weight training from a qualified instructor and get medical clearance from your doctor before you begin. Learning the proper technique will help you avoid future injuries associated with weight training. Your instructor can also give you pointers for getting the most out of your workout. Check with your school, many physical education teachers are qualified in this area.
How long you should walk, how fast and what incline all needs to be determined by you. Keeping track of your heart rate (beats per minute) during exercise is the best way to meet your fitness goals without over doing it. Heart rate training is the pre-determined heart rate an individual should reach and maintain during exercise in order to improve the efficiency of the heart and lungs. The maximum heart rate for any one individual is dependant on many factors such as age, current level of fitness and goals to be achieved through exercise. The general rule for finding your maximum heart rate is 220 minus your age. Your target heart rate would be 75% - 80% of this number.
TeenHealthFX recommends that you check with your doctor to determine what would be a safe heart rate since all individuals are different. Your doctor will also be able to advise you what to do if you have any medical conditions such as asthma.
Once you have determined a safe maximum heart rate you can begin training. If you are a beginner with the goal of improving overall fitness, losing weight or reducing stress, a healthy heart rate zone would be 50-60 percent of your maximum heart rate. You should gradually build up to a work out of 20 to 60 minutes. As your aerobic fitness increases the intensity of exercise will have to increase to keep the heart rate in the target range. Once you are in shape you can increase your performance to 70-80 percent of your maximum heart rate.
If this sounds complicated, do not worry it will come easy after some practice. In fact many aerobic machines such as treadmills, stationary bicycles and stair climbers have heart rate monitors built in. You can even buy a portable heart rate monitors that are no bigger that a wrist band, for outdoor training.
Remember if you are going to exercise regularly always do a warm up followed by some stretching. After your workout take 5-10 minutes to cool down and do some more gentle stretching. Studies have shown that people who warm up and cool down adequately have far fewer injuries.
If you would like to check with a doctor before you begin your training, and you live in northern New Jersey, you can call the Adolescent/Young Adult Center For Health at 973.889.6350 for an appointment.
TeenHealthFX applauds your desire to improve your fitness and wishes you much success.