Changes in the biomechanics of gait may alter the energy requirements of walking in Parkinson's Disease (PD). This study investigated economy of gait during submaximal treadmill walking in 79 subjects with mild to moderate PD and the relationship between gait economy and 6-minute walk distance (6？MW). Oxygen consumption (VO2) at the self-selected treadmill walking speed averaged 64% of peak oxygen consumption (VO2 peak). Submaximal VO2 levels exceeded 70% of VO2 peak in 30% of the subjects. Overall the mean submaximal VO2 was 51% higher than VO2 levels expected for the speed and grade consistent with severe impairment in economy of gait. There was an inverse relationship between economy of gait and 6MW ( , ) and with the self-selected walking speed ( , ). Thus, the impairment in economy of gait and decreased physiologic reserve result in routine walking being performed at a high percentage of VO2 peak. 1. Introduction Walking capacity is central to the performance of many activities of daily living. Difficulty with walking is one of the cardinal symptoms of Parkinson’s Disease (PD). Alterations in the biomechanics of gait, such as decreased stride length, increased stride length variability, and reduced gait speed, are common even in early stages of PD [1–3]. Most often, PD patients attempt to compensate for short steps by increasing gait cadence, thereby potentially altering energy requirements. This higher energy cost of movement is often referred to as a lower economy of gait and is a function of abnormal gait patterns that accompany aging and neurological disability. Reduced economy of gait has been associated with impaired function and fatigue in non-PD populations [4–9], but there is currently scant information on how parkinsonian gait affects energy expenditure or economy of gait using direct measures of oxygen consumption . Further, little is known about the relationship between economy of gait and mobility. Hence, the purpose of this study was to investigate economy of gait during submaximal treadmill walking in mild to moderate PD, and the relationship between economy of gait and the distance covered during the 6-minute walk (6？MW). 2. Methods 2.1. Subjects Participants for this study were recruited from the University of Maryland Parkinson’s Disease Center and the Baltimore VA Medical Center neurology clinics as part of an exercise intervention trial in PD . Inclusion criteria were (1) diagnosis of levodopa-responsive PD characterized by 2 of 3 cardinal signs (resting tremor, bradykinesia, rigidity), (2) Hoehn and Yahr (HY)  stage
J. M. Hausdorff, “Gait dynamics in Parkinson's disease: common and distinct behavior among stride length, gait variability, and fractal-like scaling,” Chaos, vol. 19, no. 2, Article ID 026113, pp. 1–14, 2009.
B. R. Bloem, J. M. Hausdorff, J. E. Visser, and N. Giladi, “Falls and freezing of Gait in Parkinson's disease: a review of two interconnected, episodic phenomena,” Movement Disorders, vol. 19, no. 8, pp. 871–884, 2004.
N. B. Alexander, G. E. Taffet, F. M. Horne et al., “Bedside-to-bench conference: research agenda for idiopathic fatigue and aging,” Journal of the American Geriatrics Society, vol. 58, no. 5, pp. 967–975, 2010.
S. J. Lewis, A. J. Barugh, C. A. Greig, et al., “Is fatigue after stroke associated with physical deconditioning? A cross-sectional study in ambulatory stroke survivors,” Archives Physical Medicine and Rehabilitation, vol. 92, no. 2, pp. 295–298, 2011.
N. B. Alexander, D. R. Dengel, R. J. Olson, and K. M. Krajewski, “Oxygen-uptake (VO2) kinetics and functional mobility performance in impaired older adults,” Journals of Gerontology—Series A Biological Sciences and Medical Sciences, vol. 58, no. 8, pp. 734–739, 2003.
W. M. Fiser, N. P. Hays, S. C. Rogers et al., “Energetics of walking in elderly people: factors related to gait speed,” Journals of Gerontology—Series A Biological Sciences and Medical Sciences, vol. 65, no. 12, pp. 1332–1337, 2010.
L. M. Shulman, L. I. Katzel, F. M. Ivey, et al., “Exercise and gait-related disability in Parkinson disease,” in Proceedings of the 63rd Annual Meeting of the American Academy of Neurology, Honolulu, Hawaii, USA, April, 2011.
S. Fahn and R. L. Elton, “Unified Parkinson's disease rating scale,” in Recent Developments in Parkinson’s Disease, S. Fahn, C. D. Marsden, D. B. Calne, and M. Goldstein, Eds., vol. 2, pp. 153–164, Macmillan Health Care Information, New York, NY, USA, 1987.
M. F. Folstein, S. E. Folstein, and P. R. McHugh, “'Mini mental state: a practical method for grading the cognitive state of patients for the clinician,” Journal of Psychiatric Research, vol. 12, no. 3, pp. 189–198, 1975.
F. M. Skidmore, S. L. Patterson, L. M. Shulman, J. D. Sorkin, and R. F. Macko, “Pilot safety and feasibility study of treadmill aerobic exercise in Parkinson disease with gait impairment,” Journal of Rehabilitation Research and Development, vol. 45, no. 1, pp. 117–124, 2008.
L. I. Katzel, J. D. Sorkin, R. F. Macko, B. Smith, F. M. Ivey, and L. M. Shulman, “Repeatability of aerobic capacity measurements in Parkinson disease,” Medicine Science in Sports & Exercise. In press.
“Metabolic calculations,” in ACSM's Guidelines for Exercise Testing and Prescription, M. H. Whaley, P. H. Brubaker, and R. M. Otoo, Eds., pp. 286–289, Lipinncott Williams and Wilkins, Philadelphia, Pa, USA, 7th edition, 2006.
J. A. Schrack, E. M. Simonsick, and L. Ferrucci, “The energetic pathway to mobility loss: an emerging new framework for longitudinal studies on aging,” Journal of the American Geriatrics Society, vol. 58, no. 2, pp. S329–S336, 2010.
E. J. Protas, R. K. Stanley, J. Jankovic, and B. MacNeill, “Cardiovascular and metabolic responses to upper- and lower-extremity exercise in men with idiopathic Parkinson's disease,” Physical Therapy, vol. 76, no. 1, pp. 34–40, 1996.
D. M. Wert, J. Brach, S. Perera, and J. M. VanSwearingen, “Gait biomechanics, spatial and temporal characteristics, and the energy cost of walking in older adults with impaired mobility,” Physical Therapy, vol. 90, no. 7, pp. 977–985, 2010.
P. L. Enrichi and D. L. Sherrill, “Reference equations for the six-minute walk in healthy adults,” American Journal of Respiratory and Critical Care Medicine, vol. 158, no. 5, part 1, pp. 1384–1387, 1998.
C. Ruggiero, E. J. Metter, V. Melenovsky et al., “High basal metabolic rate is a risk factor for mortality: the Baltimore Longitudinal Study of Aging,” Journals of Gerontology—Series A Biological Sciences and Medical Sciences, vol. 63, no. 7, pp. 698–706, 2008.
S. Frenkel-Toledo, N. Giladi, C. Peretz, T. Herman, L. Gruendlinger, and J. M. Hausdorff, “Treadmill walking as an external pacemaker to improve gait rhythm and stability in Parkinson's disease,” Movement Disorders, vol. 20, no. 9, pp. 1109–1114, 2005.
J. Mehrholz, R. Friis, J. Kugler, S. Twork, A. Storch, and M. Pohl, “Treadmill training for patients with Parkinson's disease,” Cochrane Database of Systematic Reviews, no. 1, Article ID CD007830, pp. 1–33, 2010.
T. Herman, N. Giladi, L. Gruendlinger, and J. M. Hausdorff, “Six weeks of intensive treadmill training improves gait and quality of life in patients with Parkinson's disease: a pilot study,” Archives of Physical Medicine and Rehabilitation, vol. 88, no. 9, pp. 1154–1158, 2007.