Weight Training Builds Stronger Bones And Helps Prevent Osteoporosis
Osteoporosis is an ever increasing problem worldwide as people are living longer and the population continues to age. More prevalent among women than men, some estimates report than as many as one in five American women over the age of 50 have osteoporosis. An insidious disease that weakens bone tissue, one of the worst aspects of osteoporosis is that there are no symptoms during the early stages and without a bone mineral density test it can be difficult to detect before it advances to a point where it becomes painfully symptomatic. Most learn of their condition after experiencing a bone fracture as about half of all women over the age of 50 will suffer a fracture of the wrist, hip or spine as a direct result of bone loss. Osteoporosis can be caused by many different factors which are usually lifestyle or hormone related. Excessive alcohol consumption, smoking, poor diet and inactivity are some of the known risk factors as are other circumstances which are not as controllable such as family history or hormone treatments. While there are effective treatments available for osteoporosis today the best defense is to prevent it altogether. Exercise, specifically weight bearing exercise has been shown to be an effective preventative measure against osteoporosis. In an earlier post How Muscles Get Bigger And Stronger we explored how muscles respond to weight training and in this article we will take a look how bones benefit as from resistance exercise.
The word ‘osteoporosis’ means porous bones and one can easily understand that a bone that’s porous would be weak and vulnerable to fractures. Bones weaken as a result of a process called demineralization. Demineralization occurs when our bones lose important minerals such as calcium. If left untreated our bones will no longer have the structural capacity to support the weight of our body and the forces we create when we are physically active- thus resulting in a fracture. Since we can see them all the time most of us are very much aware of our muscles, but we don’t think much of how our bones work in conjunction with them. When you flex your muscles as in a biceps curl for example, the muscles of your biceps generate force that allows you to lift the weight. This force is transferred throughout the muscle and to the tendons at both ends. The tendons are connected to the bones of your arm and cross over your elbow joint. Joints act as levers- which are rigid objects used with a pivot point to increase the amount of mechanical force our body generates to allow us to lift an object. Activation of the biceps muscles in our upper arm causes rotation of the forearm at the elbow (pivot point) which allows us to lift the weight during a curling exercise. Now according to Newton’s third law of motion, for every action there is an equal and opposite reaction. That being said since bones provide the framework for our muscles every muscular contraction will produce forces that act directly on the bones in our body.
Since bones provide the frame for our body tissue our skeleton is always under some degree of stress. As you read this blog post the force of gravity is bearing down on your bones even though you can’t really feel it. Too much stress can lead to bone damage at a microscopic level- in pretty much the same way it does in your muscles and like our muscles when bones are damaged they need to be be repaired. According to Wolff’s law, the bones in a healthy person or animal will adapt to the loads they are placed under so if the forces acting on a bone increases, the bone will remodel itself over time to become stronger and denser to be able to cope with the load that it has to bear. In essence it’s a stress response in keeping with the laws of general adaption. From a physiological point of view, stress isn’t always a bad thing as we perceive it in our everyday lives. Quite simply stress is the reaction of our body to stimulation or forces that puts it out of balance- ( a balance that we refer to as homeostasis.) If the forces are too great or too sudden – like the forces acting on your bones during a car accident or a fall from a great height- your bones can’t adapt fast enough or deal with the sudden overload and a fracture will occur. Also if a force is continuously applied through repetitive strain and your bones don’t have enough time to rest and recuperate it can also result in a fracture- in this case a stress fracture. This is what happens to many runners and aerobics aficionados after years of doing the same activity over and over again. On the other side of the spectrum, if there is a reduction in the forces on your bones, be it from being bed ridden or from living a predominantly sedentary lifestyle, your bones will remodel themselves to be weaker and less dense as a result. Just like your muscles if you don’t use it- you lose it.
Understanding How Bones Get Stronger
How your bones get stronger and denser depends not only on the degree of stress placed on them, but also on the availability of minerals such as calcium which is required to change its structure. Bones are made of collagen which is the primary form of protein found in connective tissues throughout your body. The difference between bone tissue and other forms of connective tissue is that the collagen in our bones are infused with minerals which makes it solid. When a bone is subjected to overload (from an activity like weight training for example) it experiences tiny cracks and fissures. These cracks need to be filled and reinforced so that the bone will not be damaged in the future by a similar load and thus starts a signal that mobilizes our bones to repair itself. In a process called resorption, cells called osteoclasts dissolve and break up very thin pieces of bone in the damaged area. (Think of osetoclasts as tiny construction workers who smooth over the damage done to your bones- very much the same way you would sand down a piece of wood if it was cracked before you repaired it.) After this part of the process is completed other cells called osteoblasts come in and fill in the smoothed cracks left behind by the action of the osteoclasts. (Think of osteoblasts as tiny construction workers who fill in the holes sanded down out by the osteoclasts.) This is capped off by the mineralization of the entire area which makes the bone denser and stronger than it was before- a series of actions known as bone remodeling. Bone remodeling can be affected not only by mechanical forces acting on our bodies but also by parathyroid hormones and estrogen.
How Weight Training Builds Stronger Bones
Just as muscles won’t get stronger unless there is an load applied to them that it isn’t used to dealing with, the same logic applies to our bones. That being said, to stimulate the adaptive bone remodeling process there must be some degree of overload. Doing a compound exercise like squats with weights requires a large amount of force to be generated by the muscles of your thighs and lower legs. Forces that create bending and compressive pressure within the bones of your femur (located in your upper leg), tibia and fibula (located in your lower leg). These forces create changes in fluid pressure in your bones which in turn creates the micro-fractures that trigger the adaption response for increasing bone strength. Bones can tolerate a lot more force than muscles can, and that explains why non weight bearing exercises don’t have as much impact in building stronger bones as weight training. With weight training you can progressively increase the overload factor by simply increasing the weight as you get stronger (within reasonable margins of course.) With bodyweight exercises such as aerobics or calisthenics this isn’t always possible. If you start such forms of exercise after a period of being inactive then the new stress of such exercises will have a positive effect in helping build your bones (and muscles to a degree). But after an initial period of adaptation your bones (and muscles) will have no reason to keep getting stronger as they will comfortably be able to cope with the forces incurred during body-weight exercises. Even though the exercises may be physically challenging to you, you have to keep in mind that your bones were designed to easily bear the strain of physical activity involving the weight of your body.
Studies have found that high intensity resistance training exercises (weight lifting) are an effective and feasible means to preserve bone density.1 Not only are high intensity weight training exercises useful in terms of building stronger bones, but they also improve muscle mass, strength, endurance and balance while burning extra calories and reducing body fat. [2,3,4,5,6,7,8,9,10] It can also decrease your risk of heart disease, diabetes, hypertension and reduce the incidence of depression. So pick up some iron and start lifting some weights for stronger bones, a stronger body and a stronger mind.
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6. Effects of moderate-intensity endurance and high-intensity intermittent training on anaerobic capacity and VO2max. Izumi Tabata; Kouji Nishimura, Hirai Motoki, Futoshi Ogita, Motohiko Miyachi, Kaoru Yamamoto, National Institute of Fitness and Sports in Tokyo, Japan Medicine & Science in Sports & Exercise. 28(10):1327-1330, October 1996.
7. Impact of exercise intensity on body fatness and skeletal muscle metabolism. Tremblay, A. et al., Physical Activities Sciences Laboratory, Laval University, Quebec, Canada Metabolism.1994; 43(7): 814-818
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