Lukus Klawitter M.S.

The micronutrient we are going to break down today is Calcium (Ca+).  Calcium has many important roles in the human body and is especially important in the endurance athlete to prevent bone breakdown and drive energy metabolism.

As we age, bones become more susceptible to breakdown and injury.  This is highly due to the decrease in physical activity and inadequate nutrition, where osteoclasts in the body become more active and osteoblast formation becomes less active.  This causes a breakdown of the bone and can lead to porous and brittle bones “osteoporosis”.  However, physical activity such as body weight exercises, resistance training, and even running increases osteoblast formation leading to denser and healthier bones.  Just like our skeletal muscle physiology and cardiovascular physiology our bones adapt to the stress applied and become stronger and stronger, which leads to a decrease in bone related injuries.

Well then why are bone injuries like stress fractures of the tibia or metatarsals in the feet so common in running? Well, unlike our muscles and tendons, bones are a lot less elastic. Once the stress applied becomes too great and the “stress failure” point is met, you have injury.  That being said just like training stress, the mechanical stress applied to our body needs to be added in a structured progressive overload with adequate rest for our bones to recover.  It may seem physically and physiologically easy to increase overall run volume at a very rapid rate initially, but the mechanical stress added to the body is too great for the bone to adapt and thus failure takes place.

It is true that the sport of triathlon is less impact overall then only running because cycling and swimming are non-impact, BUT this is a big decrease in osteoblast forming activity so bone density could be decreasing.  AND now this is why adequate calcium intake is very important for endurance athletes.  Swimming and cycling may be low impact but the muscles are still contracting with large amounts of force.  The muscle while cycling can create a lot more force due to the added resistance over running, and in order for the body to be able to move that muscle has to pull on bone.  Our body is a system of levers and muscles pull on bones and rotate about joints, add in some external forces like friction or fluid resistance and we get movement.  High force contractions pull forcefully on the muscle attachment point on the bone.  Pieces of bone can pull off with the muscle tendon which is called an avulsion fracture.  Daily adequate calcium intake can prevent these injuries.

Calcium also has another very important role in endurance training through energy metabolism.  Calcium has to be present in the skeletal muscle in order for ATP (energy currency) can drive the muscle to shorten and create force.  Inadequate calcium availability leads to the body leaching calcium from the bones to produce movement, which also leads to premature osteoporosis.  The importance of calcium for bone health and energy metabolism makes calcium a highly important macronutrient in endurance sports.  Athletes both male and female should aim to get 1,200-1,500mg of calcium a day in order to keep bones healthy and drive energy metabolism.

Calcium can be found in large amounts in dairy products such as milk, cheese, and yogurt.  Sardines also have high amounts; however a lot of research shows the high amounts of heavy metals in farmed fish.  There are also many plant based foods high in calcium such as fortified plant milks, chia seeds, spinach and kale etc.  A list of plant based high in calcium foods can be found here.