I just discovered there are some exercises such as swimming that are classified as no impact because you are not having any type of impact between your body and something else. Thus the low and high impact refer to the amount of impact between your body and say the floor. In high impact, the feet end up off the ground at the same time such as with jumping, running, or knee highs where as the low impact usually have one foot on ground such as with cycling, elliptical machines, hiking, yoga, and dancing. Low impact is defined as fluid motion that is easy on the joints and places less stress on the knees and joints.
There are certain circumstances when high impact exercising is better. If you want to lose weight more quickly, high impact is better because they require you to use more energy which leads to the increased burning of calories. Furthermore, these exercises tend to be more demanding and if you are willing to put in the time and energy, it helps you get in better shape faster. On the other hand, if you are getting ready for a competition such as a boxing match, or a marathon, high impact exercise prepares you better since these exercises are more efficient overall. In addition, high intensity exercises are good for building bone density especially if you are older. Finally, this type of exercise can cause a higher level of injury so if you are prone to injury, high impact is not recommended.
As far as low impact goes, it is good to use if you have been injured and need to recover without exasperating the current injury. If you've undergone joint replacement, or suffered an orthopedic injury, low impact helps you recover faster and better. In addition, if you are sore from exercising, the soreness indicates you might have stressed the area and low impact gives joints a break. Low impact exercises help improve alignment and balance because this type of exercising focuses on strengthening, stretching, balancing, and body alignment over serious calorie burning. Just because it is low impact, does not mean you won't get a good cardio workout.
Alternating high and low impact exercises is good because you are still exercising but giving your body a chance to recover from the stress of high impact. In addition, low impact builds strength and flexibility around the joints to protect them from the stress of higher impact exercises. When you stretch or do yoga at the end of a high impact session, it helps you recover better and can help build better core strength.
It is highly recommended you alternate the high and low impact exercises for the best results but if you are a beginner, have arthritis, osteoporosis, older or are pregnant, it is recommended you stick with low impact but if you are healthy, not susceptible for injury, and want to help build bone density, mix the two by alternating them. I try to alternate most days. Let me know what you think, I'd love to hear. Have a great day.