Scanning Sports Medicine
DYNAMIC POSTURAL STABILITY IN FEMALES WITH CHRONIC ANKLE INSTABILITY
In the December 2010 issue of Medicine & Science in Sports & Exercise®, researchers sought to determine whether females with chronic ankle instability (CAI) demonstrated decreased dynamic postural stability compared with control subjects in anterior, lateral, and medial jump directions (1). CAI was defined as a reported history of a moderate to severe ankle sprain, at least two episodes of subjective giving way in the past year, and decreased self-reported ankle function. The control group reported less than or equal to one previous mild to moderate ankle sprain, no episodes of giving way, and no decrease in ankle function. Neuromuscular control can be measured by dynamic postural stability using well-researched tests such as the single leg landing test and the dynamic postural stability index (DPSI). The single leg landing task is thought to be both functional and demanding, since it replicates sports activity and requires strength, proprioception, and neuromuscular control. DPSI is used to quantify those abilities and indicate an individual's ability to maintain balance while transitioning from a dynamic to a static state as a functional measure of neuromuscular control. Stability indices are calculated for the anterior-posterior (APSI), medial-lateral (MLSI), and vertical (VSI) directions, in addition to a composite score that combines the three directions (DPSI). Prior research has identified differences in DPSI scores between anterior and lateral and diagonal jump directions in healthy subjects, but no previous data exist as to whether subjects with CAI demonstrate stability deficits in jump directions other than anterior. The study measured maximal vertical jump height in anterior, lateral, and medial directions. Participants then jumped at 50% max height in the three directions, landed on the involved limb, and balanced for 10 s. Ground reaction forces were collected at 1200 Hz and filtered. The most important finding of this study was that the CAI group demonstrated statistically significantly greater VSI and DPSI scores than controls in the anterior and lateral jump directions. This indicates that the CAI group had decreased postural stability in both jump directions. Bottom line: Females with CAI had decreased dynamic postural stability compared with controls in the anterior and lateral jump directions. Clinically, this translates into the need for incorporating other jump directions into dynamic postural stability testing to reveal such neuromuscular deficits, to improve rehabilitation strategies, and to better assess a patient's ability to stabilize in more chaotic real-life environments.
GLYCEMIC INDEX AND GLYCEMIC LOAD: THEIR APPLICATION IN HEALTH & FITNESS
The November/December 2010 issue of ACSM's Health & Fitness Journal® provides a review of the current research pertaining to the glycemic index (GI) and its impact on metabolism and exercise performance, as well as reviews the concept of glycemic load (GL) (2). A plethora of information exists regarding the recommended timing and amount of carbohydrate (CHO) to be ingested before, during, and after exercise. Debate still exists, however, as to which type of CHO will provide athletes with the most benefit during each of these phases. The preexercise phase seems to support the use of low GI foods. This largely is due to the resultant decrease in postprandial hyperglycemia and hyperinsulinemia. This causes an increase in free fatty acid oxidation and potentially better maintenance of plasma glucose concentrations, leading to a more sustained availability of CHO during exercise. During exercise, athletes typically consume CHO in the form of sports drinks or sports bars. It has been found that once a standard amount of CHO is consumed, typically either 2 g CHO·kg−1 body mass or ∼6% CHO solution, the typical responses seen with low GI preexercise ingestion are overridden. Performance enhancements during this phase are due to exogenous CHO intake rather than any GI-related benefit. In the postexercise phase, it is crucial to replenish muscle glycogen stores. While a high GI meal can increase the body's glucose response, once sufficient CHO has been ingested, no differences exist in glycogen storage between high and low GI CHO ingestion. The concept of GL, while still in its infancy, is gaining momentum as yet another way to assist in maximizing fat oxidation and overall performance. Bottom line: Ingestion of low GI CHOs can increase fat oxidation and potentially increase endurance performance during subsequent exercise. Postexercise, high GI CHO ingestion can speed up glycogen repletion. Because GL incorporates both the GI and serving sizes, GL may be a better predictor of one's glycemic response than GI alone.
1. Brown CN, Bowser B, Orellana A. Dynamic postural stability in females with chronic ankle instability. Med. Sci. Sports Exerc
. 2010; 38(12):[Epub ahead of print].
2. Wong SH, O'Reilly J. Glycemic index and glycemic load: their application in health and fitness. ACSM's Health & Fitness Journal
. 2010; 14(6):18-23.