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Introduction. Spinal and bulbar muscular atrophy (SBMA) is a neuromuscular disorder that leads to progressive weakness of bulbar and extremity muscles. Dynamic balance during functional tasks has not been reported in people with SBMA. Objectives. (1) To evaluate the ability to safely complete a forward lunge (FL), step quick turn (SQT), and step up and over (SUO), (2) to determine the presence and severity of dynamic balance impairments by comparing performance to normative data, and (3) to investigate the relationship between lower extremity strength and ability to complete each task. Design. Cross-sectional analysis. Participants. Fifty-three people with SBMA were included in a cross-sectional analysis. Normative datasets provided by the NeuroCom manufacturer and isometric strength literature facilitated patient comparisons. Outcome Measures. Force plate-based dynamic balance measures included FL (distance, impact index, contact time, and force impulse), SQT (turn time and turn sway), and SUO (lift up index, movement time, and impact index). Maximal isometric contractions of knee extensors, ankle dorsiflexors, ankle plantar flexors, and hip extensors were measured with fixed frame dynamometry. Results. The most difficult test, per completion rate, was SUO (52%), followed by FL (57%) and SQT (65%). t -tests revealed significant abnormalities in eight of nine balance variables ( p < 0.05 ) accompanied by large Cohe n ’ s D effect sizes ≥ 0.8 . Receiver operating characteristics analysis showed knee extensor (SUO 95% CI =0.78–1.00, SQT 95% CI =0.64-0.92) and ankle plantar flexor strength (SUO 95 % CI = 0.75 – 0.99 , SQT 95 % CI = 0.64 − 0.92 ) significantly discriminated the ability to perform SUO and SQT tests with acceptable to excellent areas under the curve. Conclusions. Considerable dynamic balance abnormalities were observed. Lower extremity strength helps explain low test completion rates. Patients modified task movement patterns, enabling safe task performance. Study results can help direct patient care and future protocol design for people with SBMA.

Purpose. The adult myopathy assessment tool (AMAT) is a performance-based battery comprised of functional and endurance subscales that can be completed in approximately 30 minutes without the use of specialized equipment. The purpose of this study was to determine the construct validity and internal consistency of the AMAT with a sample of adults with spinal and bulbar muscular atrophy (SBMA).Methods. AMAT validity was assessed in 56-male participants with genetically confirmed SBMA (mean age, 53 ± 10 years). The participants completed the AMAT and assessments for disease status, strength, and functional status.Results. Lower AMAT scores were associated with longer disease duration (r=-0.29;P<0.03) and lower serum androgen levels (r=0.49–0.59;P<0.001). The AMAT was significantly correlated with strength and functional status (r=0.82–0.88;P<0.001). The domains of the AMAT exhibited good internal consistency (Cronbach’sα = 0.77–0.89;P<0.001).Conclusions. The AMAT is a standardized, performance-based tool that may be used to assess functional limitations and muscle endurance. The AMAT has good internal consistency, and the construct validity of the AMAT is supported by its significant associations with hormonal, strength, and functional characteristics of adults with SBMA. This trial is registered with Clinicaltrials.gov identifierNCT00303446.