Relationships between plantar flexor muscle stiffness, strength, and range of motion in subjects with diabetes-peripheral neuropathy compared to age-matched controls.

STUDY DESIGN

Descriptive study to compare relationships between muscle performance measures in 2 subject groups.

OBJECTIVES

To determine the relationships between plantar flexor (PF) muscle stiffness, strength (concentric peak torque), and dorsiflexion (DF) range of motion (ROM) in subjects with diabetes who have peripheral neuropathy (n = 17, 10 men, 7 women; age = 58 +/- 11 years) and age-matched controls (n = 17, 10 men, 7 women; age = 62 +/- 6 years).

BACKGROUND

The relationships between muscle stiffness, strength, and joint ROM have not been clearly established. Furthermore, the effect of neuromuscular pathology on these relationships is unknown.

METHODS AND MEASURES

PF stiffness and strength measurements were obtained with an isokinetic dynamometer. DF ROM was measured with a goniometer. A Pearson correlation matrix was constructed for each subject group using stiffness, strength, and ROM variables. The percent contribution of passive torque to total torque was computed at 2 joint angles.

RESULTS

In subjects with diabetes and peripheral neuropathy (DM-PN) peak concentric PF torque was positively correlated with passive torque at 5 degrees DF (r = 0.77), Stiffness #1 (r = 0.58), and Stiffness #2 (r = 0.50). The percentage of passive PF torque at 5 degrees DF was greater in subjects with DM-PN, compared to control subjects (29.3 +/- 9.4% versus 12.6 +/- 5.9%).

CONCLUSIONS

The positive correlation between PF stiffness and strength, and the greater percentage of passive PF torque in subjects with DM-PN suggest that patients with decreased strength may use passive torque to maximize total torque. Therefore, treatment methods designed to decrease stiffness should be used cautiously.