ORIGINAL ARTICLE Reliability of Measurements of Tongue and Hand Strength and Endurance Using the Iowa Oral Performance Instrument with Healthy Adults Valerie Adams • Bernice Mathisen • Surinder Baines • Cathy Lazarus • Robin Callister Received: 14 February 2013 / Accepted: 5 August 2013 Ó Springer Science+Business Media New York 2013 Abstract The purpose of this study was to investigate the reliability of tongue and handgrip strength and endurance measurements in healthy adults using the Iowa Oral Per- formance Instrument. Fifty-one healthy participants (21 males, 30 females; age range = 19–57 years) were tested on four occasions 1 week apart to determine test–retest reli- ability. The primary outcome measures were isometric tongue and handgrip strength (best of three trials) and sustained isometric endurance. Small increases (changes in group mean) in both anterior (1.7 %) and posterior (2.5 %) tongue strength and handgrip strength (5 %) between weeks 1 and 2 were observed with no change in subsequent weeks, suggesting that there is only a small learning effect for these measurements. The within-subject variation (mean-typical error expressed as a coefficient of variation [CV]) indicated higher than desirable initial variation for anterior (CV 10.8 %) and posterior (CV 11.8 %) tongue strength and handgrip strength (CV 15.2 %) but this was reduced in weeks 2–4. Intraclass correlation coefficients (ICC) indicated acceptable and improved reliability for both anterior (ICC 0.77–0.90) and posterior (ICC 0.79–0.86) tongue strength and handgrip strength (ICC 0.69–0.91) after week 1. Additional exploratory analyses were conducted with a subset of data to determine whether two values within 5 kPa (tongue) or 15 kPa (handgrip) provide superior strength reliability. Neither tongue nor hand endurance measurements were sufficiently reliable. These findings suggest that tongue and handgrip strength values demonstrate acceptable reliability, especially if familiarization is provided. Further investigation is needed to reduce sources of variability in tongue endurance measurements. Keywords Reliability Á Test–retest Á Anterior Á Posterior Á Tongue Á Deglutition Á Deglutition disorders Introduction Appropriate tongue strength is essential for the oral and pharyngeal phases of swallowing and contributes to the formation, placement, and manipulation of a bolus within the oral cavity and propulsion into the pharynx [1]. Examination of tongue strength is a frequent component of the clinical assessment of swallowing by speech-language pathologists. Such assessment is usually based on sub- jective judgment of the force being applied by the tongue against resistance provided by the speech-language V. Adams Á R. Callister (&) Priority Research Centre in Physical Activity and Nutrition, Faculty of Health and Medicine, School of Biomedical Sciences and Pharmacy, The University of Newcastle, University Drive, Callaghan, NSW 2308, Australia e-mail: Robin.Callister@newcastle.edu.au B. Mathisen Faculty of Health Sciences, LaTrobe Rural Health School, LaTrobe University, Bendigo, VIC 3552, Australia S. Baines Faculty of Health and Medicine, School of Health Sciences, The University of Newcastle, University Drive, Callaghan, NSW 2308, Australia C. Lazarus Department of Otorhinolaryngology Head & Neck Surgery, Albert Einstein College of Medicine of Yeshiva University, Bronx, NY, USA C. Lazarus Thyroid Head and Neck Research Center, Thyroid Head and Neck Cancer (THANC) Foundation, Beth Israel Medical Center, 10 Union Square East Suite 5B, New York, NY 10003, USA 123 Dysphagia DOI 10.1007/s00455-013-9486-5