Q: I recently walked a half marathon and did pretty well time wise, but when I finished my shins really began aching. I iced them when I got home but the next morning I noticed bruising on both legs just below my knees where it seems the muscle attaches. It is very painful to the touch and to walk. Could I have torn the muscle just by walking? How can I prevent this in the future?

A: The presence of bruising without impact indicates that most likely muscle tearing did occur on a micro level from the half marathon. Muscles attaching in the area you indicated are foot decelerators, which slow down and control the placement of forefoot right after heel strike has occurred. To prevent this kind of reaction in the future make sure you are conditioning the calf and leg muscle groups for endurance, have adequate arch support in your shoes to assist in decelerating your feet and supporting them during mid-stance and toe off. The other factor to consider is your walking gait pattern. A longer gait has increased heel strike and requires more foot deceleration force from the muscles in the front section of your calf region. If your gait is long I would recommend shortening your stride and work toward a quicker leg speed to maintain the same pace. Good luck in your training. I hope you have a great season.

— Bryan Baisinger, DC

Q: I've heard many times that applying daily sunscreen is one of the best ways to prevent skin cancer and avoid the signs of aging. However, my understanding is that sunscreen is made out of some pretty harsh chemicals. Can applying these chemicals daily cause other types of damage to the skin and body?

A: There is no evidence that daily applications of sunscreen cause any kind of damage to the skin or other body organs. People with "sensitive" skin sometimes develop an irritant reaction to certain chemical sunscreen ingredients and for that reason sunscreens containing the physical sunblocking agents titanium dioxide or zinc oxide are a good choice. Those two ingredients are less irritating to the skin. It is also possible to develop an allergic contact rash to certain sunscreen ingredients. If you develop a rash after sunscreen application you should consult a dermatologist. The health benefits from using a sunscreen far outweigh any potential adverse effects.

— Diane Baker, MD

This issue’s experts:
Bryan Baisinger, DC, is owner of Clearwater Chiropractic & Massage. To contact Dr. Baisinger call 503-279-0205 or email bryan@clearh2o.org.

Diane Baker, MD, is in full-time private practice in Portland. She holds a clinical appointment as a Clinical Professor, Department of Dermotology at Oregon Health Sciences University in Portland.