T.H. IJZERMANa, T. MELAIa,b, K. MEIJERa, N.C. SCHAPERc, P.J.B. WILLEMSa, A.L.H. DE LANGEb, H.H.C.M. SAVELBERGa
aNutrition and Toxicology Research Institute Maastricht, Dept. Health, Medicine and Life Sciences, University Maastricht
bFontys University of Applied Sciences, Eindhoven, The Netherlands
cCardiovascular Research Institute Maastricht, Academic Hospital
Abstract. The purpose of this study was to investigate the effect of diabetic polyneuropathie (DPN) on muscle strength of the lower limb and mobility. Based on previous studies we expect that diabetes leads to a loss in muscle strength and that this process will be enhanced by neuropathy. Moreover, it has been hypothesized that muscle weakness is a main factor in limitations of the mobility.
The study enrolled 62 subjects: 27 DPN patients, 16 age matched diabetic type 2 patients (DM2) without DPN (DC) and 19 healthy subjects (C). They performed isometric knee and ankle strength tests on a dynamometer. Mobility was determined from a timed ‘get up and go test’, a six minute walk test and the PASE (physical activity scale for the elderly) questionnaire. Healthy elderly had significantly higher muscle strength compared to the DC and DPN groups (p<0.01). No significant differences were found between DC and DPN. For both groups DC en DPN muscle weakness strongly correlates with the level of mobility in daily life (p<0.05 for all outcome parameters).Muscle weakness itself seems to be a strongly predictor for the decline in mobility. Moreover, DPN does not lead to a larger decrease of muscle weakness compared to DM2 patients.
Keywords. type 2 diabetes mellitus, polyneuropathy, muscle strength, mobility.
1. Introduction
Impaired mobility is a major health problem affecting many subjects with diabetes mellitus (DM). It is associated with loss of quality of life and it is a strong predictor for poor health outcomes. Reduced lower extremity muscle function, as a consequence of diabetic polyneuropathy (DPN), is a major cause of impaired mobility. The loss of motor and sensory nerve functions can lead to loss of muscle mass and strength.
The purpose of the present study was to compare mobility and muscle strength in the lower extrimities in DPN and type 2 diabetes mellitus (DM2) patients and to investigate whether mobility and muscle strength are related. The disablement process in DM patients is often progressive and results in worsening of the impairments. Based on previous studies [1,2] we expect that DM2 causes a decline of muscle strengh and that due to motor and sensory nerve damage DPN will enhance this process. It has been hypothesized that muscle weakness is an important factor in the limitation of mobility.
Rehabilitation: Mobility, Exercise and Sports L.H.V. van der Woude et al. (Eds.)
IOS Press, 2010
© 2010 The authors and IOS Press. All rights reserved.
doi:10.3233/978-1-60750-080-3-137
137
2. Subjects and Methods Subjects
DPN patients (n=27), age matched DM2 patients without DPN (DC) (n=16) and healthy age matched subjects (C) (n=19) performed maximal, voluntary, isometric knee-joint extensor and flexor and ankle plantar and dorsal flexor strength tests in a dynamometer. The diagnosis of DPN was based on a standardized clinical neurological examination. [3]
Methods Mobility tests
Mobility was determined from a timed ‘get up and go’ test (TGUG), a six minute walk test (6MWT) and the physical activity scale for the elderly questionnaire (PASE).
Isometric knee and ankle tests
The subjects were instructed to develop subsequently a maximal extending and a maximal flexing knee joint moment in 5 different angles of the right leg; 100°, 90°, 70°, 50° and 30° were 0° is a fully extended leg. The hip angle was constantly at 90°. The maximal dorsal and plantar ankle joint moments were determined in five different angles; maximal dorsal flexion, 90°, 110°, 130° and maximal plantar flexion. The maximal joint moment were normalized for body weight. Optimal angles were determined by meaning of a second degree polynomial regression through the normalized strength data.
3. Results
With respect to mobility a decreasing trend from C to DC and from DC to DPN was found (Table 1).
Table 1. Differences in mobility and maximal torques and optimal angles of the ankle and knee
Mobility DPN DC C
*Different from Control (p≤0.05). #Different from DM (p<0.01)
The 6MWT showed significant differences between every single group (p<0.01). The TGUG test resulted in significant difference between the DPN and C group (p≤0.05);
no significant differences were found between the three groups regarding to the PASE questionnaire. A clear tendency in decreased mobility was observed in the DC and DPN group, where DPN showed the lowest mobility scores (Table 1).
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Overall muscle strength was significantly higher in healthy elderly than in the DC and DPN group (p<0.01)(table 1). No significant differences were found between the DC and DPN group. No significant differences were found with respect to the optimal knee and ankle angles (table 1). The degree of muscle weakness correlated strongly with the level of mobility (figure 1).
maximal dorsal flexion torque (Nm/kg)
Figure 1. Correlation between maximal dorsal ankle torque and 6MWT.
4. Discussion
We hypothesized that muscle strength and mobility in DM2 patients is impaired and that DPN aggravates his impairment. We have shown that DM2 patients have decreased muscle strength compared to healthy age matched elderly. Nevertheless, the presented data suggest that DPN has no additional effect on muscle strength above diabetes itself. In other words, the diminished nerve function in the lower extremities does not cause decreased muscle strength. But yet, patients with DPN walk less far in spite of relative similar muscle strength. These data suggest that the decreased mobility in DPN patients, compared to DM2 patients, is not due to muscle weakness but to other features like diminished sensory and motor nerve functions.[1]
5. Conclusion
Muscle weakness itself is associated to the decline in mobility. Moreover it seems that DPN does not lead to a larger decrease of muscle strength compared to patients with DM2. More research is needed to determine the influence of nerve damage in DPN patients on muscle strength and to find an explanation for a reduced mobility in DPN subjects compared to DM.
References
[1] C.S. Andreassen et al, Muscle weakness: a progressive late complication in diabetic distal symmetric polyneuropathy, Diabetes 55 (2006), 806-12.
[2] A.A. Sayer et al, Type 2 diabetes, muscle strength, and impaired physical function: the tip of the iceberg?, Diabetes Care 28 (2005), 2541-2.
[3] G.D. Valk et al, The assessment of diabetic polyneuropathy in daily clinical practice: reproducibility and validity of Semmes Weinstein monofilaments examination and clinical neurological examination, Muscle Nerve 20 (1997), 116-8.
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