«

»

Mar
04

The Female Runner and Body Mass Index

Dr. Mackarey's Health & Exercise Forum

PIAA Spring Sports (Track & Field) Begins today, March 4Th! To prevent injuries such as shin splints and stress fractures, participants, especially female athletes, must take time to properly prepare for your event.

Have you notice more local running enthusiasts in the past few years? Moreover, have your noticed that most of the runners are women? Scranton Running Company has contributed to NEPA’s participation in a national trend; more women are engaged in running than men! Female runners account for 9.7 million runners (57%) while 7 million males run on a national level.

With this surge, the female runner has been subjected to a host of related injuries, including shin splints, which often lead to stress fractures. New research has found that stress fractures may be related to the loss of weight and body mass associated with the sport.

A recent study from Ohio State University found that female runners with a Body Mass Index (BMI) below 19 may have a higher risk of developing stress fractures than women with a BMI of 19 or above. Furthermore, the study also found that these women took longer to recover from these injuries.

According to Timothy Miller, MD, “When body mass index is very low and muscle mass is depleted, there is nowhere for the shock of running to be absorbed other than directly into the bones. Until some muscle mass is developed and BMI is optimized, runners remain at increased risk of developing a stress fracture,”

The study also found that female runners with a BMI of 19 or higher with severe stress fractures required 13 weeks to recover from their injuries and return to running. Runners with a BMI lower than 19, however, took more than 17 weeks to recover.

They concluded that women should know their BMI and consult with a medical professional to maintain a healthy number. Additionally, women should cross-train and include resistance training to improve the strength and muscle mass of the lower extremities to prevent injury.

The current BMI wisdom, according to the National Institutes of Health, is 19.8 for men and 24 for women, however, strong and competitive women tend to have a BMI of 26. A BMI of 18 is considered malnourished.

What is BMI?

Body mass index (BMI) is a measure of body fat based on height and weight of adult men and women over 20 years of age, according to the National Institutes of Health.

BMI = (weight in pounds / height in inches squared) X 703)

Example 1: a person who weighs150 pounds and is 68 inches (5 feet 8 inches) tall has a BMI of 22.8

Example 2: a person who weighs 110 pounds and is 66 inches (5 feet 5 inches) tall has a BMI of 17.7

Underweight      < 18.5%

Normal weight      18.5 to 24.9%

Overweight      25 to 29.9%

Obesity            30 and over

What is a stress fracture?

A stress fracture is fatigue damage to bone with partial or complete disruption of the cortex of the bone from repetitive loading. While standard x-rays may not reveal the problem, a bone scan, and MRI will. It usually occurs in the long bones of the leg, mostly the tibia (shin bone) but also the femur (thigh) and foot. Occasionally, it occurs in the arm.

Who is at risk for stress fractures?

FEMALE RUNNERS WITH BMI LOWER THAN 19 – is a primary risk factor.

10-21% of all competitive athletes are at risk for stress fractures. Track, cross country and military recruits are at greatest risk. Females are twice as likely as males to have a stress fracture. Other athletes at risk are: sprinters, soccer and basketball players, jumpers, ballet dancers are at risk in the leg and foot. Gymnasts are also vulnerable in the spine while rowers, baseball pitchers, golfers and tennis players can experience the fracture with much less frequency in the ribs & arm.

The problem is much more prevalent in weight bearing repetitive, loading sports in which leanness is emphasized (ballet, cheerleading) or provides an advantage (distance running, gymnastics).

Stress fractures usually begin with a manageable, poorly localized pain with or immediately after activity such as a shin splint. Over time, pain becomes more localized and tender during activity and then progresses to pain with daily activity and at rest.

Other Causes of Stress Fractures

  • Overuse, Overload, Over-training – is the number one cause. Running too many miles with too much intensity with too much frequency is the perfect formula.
  • Inadequate Fitness Level – or activity level prior to the stress fracture. For example, the high school runner takes the summer off and then quickly accelerates his/her program to quickly for cross-country in August/September.
  • Poor Biomechanics – when your feet hit the ground the forces are absorbed and transferred to the rest of the body. If the biomechanics of feet are not perfect, then the forces are not absorbed and another body part bears too much force. For example, flat or pronated feet poorly absorb the shock and pull the tendons of the foot and shin.
  • Recent Change in Training Schedule – sudden increased intensity or speed
  • Recent Change in Running Surface – sudden change to a hard or soft surface
  • Recent Change in Footwear – shoes too hard or too soft, too much control or too little control, too much pronation or too much supination
  • Overweight – running with an extra 10 pounds and attempting to return to running as a method of weight loss
  • Underweight – the underweight female athlete is at high risk for stress fractures. If underweight and have a history of menstral irregularities or and eating disorder, the risk of stress fracture increases significantly
  • History of Stress Fractures – makes the athlete two times as likely to have another

Prevention & Treatment

  • Maintain Ideal BMI – 24 for female runners
  • If Overweight – gradual exercise with diet, not too much too quickly

         Mix run & walk every 10 minutes

  • If Underweight – improve diet maintain healthy body fat%
  • Alternate Training – cross train with non-weight bearing activities: bike, swim, elliptical
  • Perform lower body weight training – to strengthen the muscles of the lower body, thighs, knees, ankles, feet.
  • Gradually Build Up Fitness Level – wean into activity 1-2 miles, then add ½ mile at a time
  • Correct Biomechanics – Orthotics, Running shoes, see a Podiatrist
  • Gradual Change in Training Schedule
  • Gradual Change in Surfaces – ½ run on soft surface, ½ run on hard surface
  • Gradual Change in Foot ware – walk in new shoes first, then run 1-2 miles
  • Consult Family Physician/Orthopedic Physical Therapist/Nutritionist

Source: Ohio State University, Science Daily

Visit your doctor regularly and listen to your body.      

NEXT MONDAY – Read Dr. Paul J. Mackarey “Health & Exercise Forum!”   

This article is not intended as a substitute for medical treatment. If you have questions related to your medical condition, please contact your family physician. For further inquires related to this topic email: drpmackarey@msn.com

Paul J. Mackarey PT, DHSc, OCS is a Doctor in Health Sciences specializing in orthopaedic and sports physical therapy. Dr. Mackarey is in private practice and is an associate professor of clinical medicine at Geisinger Commonwealth School of Medicine.