MÜNDERMANN, A., B. M. NIGG, R. N. HUMBLE, and D. J. STEFANYSHYN. Orthotic Comfort Is Related to Kinematics, Kinetics, and EMG in Recreational Runners. Med. Sci. Sports Exerc., Vol. 35, No. 10, pp. 1710–1719, 2003.
Purpose: The purpose of this study was to determine the relationship between differences in comfort and changes in lower extremity kinematic and kinetic variables and muscle activity in response to foot orthoses.
Methods: Twenty-one recreational runners volunteered for this study. Three orthotic conditions (posting, custom-molding, and posting and custom-molding) were compared with a control (flat) insert. Lower extremity kinematic, kinetic, and EMG data were collected for 108 trials per subject and condition in nine sessions per subject for overground running at 4 m·s−1. Comfort for all orthotic conditions was assessed in each session using a visual analog scale. The statistical tests used included repeated measures ANOVA, linear regression analysis, and discriminant analysis (α = 0.05).
Results: Comfort ratings were significantly different between orthotic conditions and the control condition ([lower, upper] confidence limits; posting: [−3.1, −0.8]; molding: [0.4, 3.4]; and posting and molding: [−1.1, 1.9]); 34.9% of differences in comfort were explained by changes in 15 kinematic, kinetic, and EMG variables. The 15 kinematic, kinetic, and EMG variables that partially explained differences in comfort classified 75.0% of cases correctly to the corresponding orthotic condition.
Discussion: In general, comfort is an important and relevant feature of foot orthoses. Evaluations of foot orthoses using comfort do not only reflect subjective perceptions but also differences in functional biomechanical variables. Future research should focus on defining the relationship between comfort and biomechanical variables for material modifications of footwear, different modes of locomotion, and the general population.
Foot orthoses are often used by recreational runners with the goal to prevent running related injuries, to support the rehabilitation process after injuries, to increase comfort, and/or to improve performance. Foot orthoses are frequently custom-molded, and the reported success rates are between 50 and 90% (6,7). Foot orthoses have been proposed to provide comfort (35), to reduce frequency of movement related injuries (11), to align the skeleton (15), to provide improved cushioning (15), to improve sensory feedback (27), to reduce muscle activity (22), and/or to reduce joint moments (5).
Comfort is a quantity that is clear and obvious for the footwear user. Most people can quickly identify comfortable or uncomfortable shoe and orthotic situations. Comfort is a requirement used by clinicians to determine the appropriateness of foot orthoses. If foot orthoses were not comfortable to an individual, this person would discontinue wearing the foot orthoses and potential benefits of the foot orthoses would be lost. Therefore, comfort is an important aspect of foot orthoses. However, the factors that are important for orthotic comfort are not well understood.
Factors that are assumed to influence orthotic comfort include foot shape, fit between footwear and foot, skeletal alignment, foot sensitivity, joint motion, forces acting on the musculoskeletal system, and muscle activity. Comfort of footwear has been related to subject characteristics such as foot shape, skeletal alignment, and foot sensitivity (17,20). Individual differences in these subject characteristics were reflected in differences in the individual comfort perception.
Footwear modifications including material and shape modifications have been shown to affect functional variables including lower-extremity kinematics (7,25), kinetics (24), and muscle activity (32) during locomotion. Additionally, it has been shown that footwear modifications can be perceived by subjects (13,26), that they affect subjective comfort for locomotor tasks such as running and walking (17,19,20), and that the effects may be different between walking and running (17). Consequently, differences in comfort may be related to changes in these functional variables in response to footwear modifications for specific movement tasks. However, to date, no conclusive evidence has been provided as to whether comfort is in fact related to lower extremity kinematics, kinetics, and muscle activity during locomotion.
The purpose of this study was to determine the relationship between differences in comfort and changes in lower extremity kinematic and kinetic variables and muscle activity in response to foot orthoses. It was hypothesized that differences in comfort can be partially explained by changes in lower extremity kinematics, kinetics, and muscle activity.