THE SAFETY AND EFFICACY OF USING A DOUBLET FOR DETERMINATION OF CENTRAL ACTIVATION FAILURE IN ELDERS POST HIP FRACTURE. Alyson Schular1; Jeannie Wang*2; Marty Eastlack3 1. Rehabilitation, Montgomery Hospital Medical Center, Norristown, PA; 2. Physical Therapy, MossRehab Hospital, Philadelphia, PA; 3. Physical Therapy, Arcadia University, Glenside, PA PURPOSE: To develop a safe and effective protocol using doublet electrical stimulation superimposition technique (IDT) to investigate CAF of the quadriceps femoris muscle in elders after hip fracture. BACKGROUNDS/SIGNIFICANCE: The use of superimposed electrical stimulation has been well documented in the literature as a valid means to detect central activation failure (CAF) in human muscle. Previous studies have shown that with normal aging there are morphologic, physiologic and central activation changes that limit an individual’s ability to produce force. CAF research on elders has targeted “healthy” and “active” subjects, therefore little is known of the deficits present in the hip fracture population or populations where osteopenia exist. SUBJECTS: A sample of convenience of seven elderly subjects ranging from 15-47 months post-hip fracture (mean=29 mos.) was recruited. Three subjects had left-sided fractures and four had right-sided fractures. Ages ranged from 64-85 (mean=78 yrs.). The mean Mini-Mental State Exam score was 29 (range of 27-30) and the mean Physical Activity Scale for the Elderly score was 100.8 (range of 63.3-160.7). METHODS AND MATERIALS: Consent was obtained and demographic data was collected. Subjects were positioned on the Kincom dynamometer with two electrodes placed on the proximal and distal quadriceps femoris. The testing trial consisted of the subject performing a maximal volitional isometric contraction (MVIC), where once the force had plateaued the subjects received a doublet electrical stimulation, which was once again administered at rest. The parameters for the doublet technique were: a train duration of 16 ms, a stimulation rate of 100 Hz, a stimulation duration of 2 ms, and an individually titrated supramaximal intensity (range 130-150 v). A session consisted of three trials with two-minute rest periods in between. This protocol was used for both the hip fracture and reliability subjects. Reliability testing was done in a sample of convenience of 3 young healthy subjects ranging in age from 23-25 (mean age=24 yrs.). ANALYSES: The voluntary muscle activation ratio during MVIC doublet superimposition testing was calculated as: 1-(force augmentation from stimulation / force of stimulation at rest), where 1.0 represents full activation and anything < 1.0 represents incomplete activation. The best trial was used to quantify MVIC force and degree of central activation failure. MVIC forces were also normalized to the individual’s BMI. Descriptive statistics and ICC (3,1) were used. RESULTS: CAF was detected in this population. The mean IDT was 0.71 ± 0.17, therefore there was 29% CAF of the quadriceps femoris. Mean MVIC was 510 ± 541.06 N with a range of 205.86-1719.38 and the mean force when normalized to the BMI was 20.40 ± 20.03 N/(kg/m2) with a range of 7.35-65.05. None of the hip fracture patients reported any difficulty with the test nor were there any complications during or as a result of the doublet testing in this population sample. High inter-rater reliability for data analysis was shown (0.92-1.0) using intra-class correlation coefficients (ICC 3,1). Reliability of the testing protocol was also shown to be high (ICC (3,1)=0.86-0.95). CONCLUSIONS: CAF was detected among the hip fracture subjects investigated. Both the testing protocol and data analysis were reliable. There were no complications or complaints by participants throughout the study. Doublet electrical stimulation was found to be safe amongst the seven hip fracture subjects with respect to our inclusion criteria. CAF appears to be a critical component of the strength deficit found among the post hip fracture population. With further research perhaps more efficacious interventions that target increasing central activation of muscle can be utilized to improve outcomes and quality of life. FUNDING SOURCE: Supported by the Arcadia Physical Therapy Alumni Association and the Ellington Beavers Award KEYWORDS: Geriatric, central activation failure, osteopenia, electrical stimulation/muscle performance, hip fractures Copyright 2009 by the American Physical Therapy Association. Requests for reprints should be directed to the corresponding author of the article. Educators, students, and other academic customers may receive permission to reprint copyrighted material from Physical Therapy (ISSN 1538-6724) by contacting the Copyright Clearance Center Inc, 222 Rosewood Dr, Danvers, MA 01923. Other types of customers who want permission to reprint should contact the APTA Editorial Office, Attn: Physical Therapy.