Forty two million Americans, approximately, are considered runners today and half of those are over 35 years-old. Despite the benefits that running brings to older individuals health, there are an increase number of running-related injuries in this population. This high rate of injuries may be partly due to altered running mechanics.
This study aimed to evaluate the surface electromyography (EMG) of gluteus medius and the peak of hip adduction at stance phase in young, middle-aged and elderly runners during running on a treadmill.
Eighteen subjects were allocated into three groups. Group 1 (R1) included six men aged between 18 and 35, group 2 (R2), with six men aged between 36 and 60 years and Group 3 (R3), with six men aged over 61 years. As inclusion criteria, the subjects should run more than 10 kilometres per week and be a rear foot striker. The exclusion criteria were any incidences of injury in the three months prior to the experimente and musculoskeletal alterations. EMG was simultaneously recorded with kinematics at 2400Hz using wireless surface EMG electrodes (TrignoTM Wireless System, DelSys, Inc., Boston, MA, USA) and Qualisys Motion Capture System (Qualisys Medical AB, Sweden) with seven cameras and a sampling frequency of 240Hz. The EMG and kinematic signals were processed using custom MATLAB software. The average of 5 stance phases of each condition from the dominant lower limb was analysed. One-way ANOVA test was performed to comparison between groups and post hoc comparisons were performed using Bonferroni adjustments (α = 0,05).
Significant differences were found for the peak of hip adduction between M1 and M2 (higher values for M2, p = 0.006) and between M1 and M3 (higher values for M3, p = 0.005). In addition, significant differences were found for the muscle activation of gluteus medius between M1 and M2 (higher values for M1, p = 0.001) and M1 and M3 (higher values for M1, p = 0.005). There were no significant differences between groups M2 and M3 for both variables evaluated.
Musculoskeletal injuries in runners are common and may be attributed to the inability to control the hip and pelvic movements in the frontal plane. This lack can be from dysfunction of the gluteus medius. Thus, studies shows that an increase of hip adduction is associated with an increase in the quadriceps angle (Q angle) and this contributes to dynamics knee valgus. Since the Q angle reflects the frontal plane forces acting on the patella, biomechanics changes of the lower limb in the frontal plane may affect the patellofemoral joint. Therefore, there is an increase in the lateral forces acting on the patella, which can lead to a maltracking and can result in an increased contact, leading to articular cartilage degradation and pain over time. Therefore, the older runners showed an increase in hip adduction peak and a decrease of gluteus medius activation which are risk factors for certain injuries. These changes can generate an overload, mainly in the knee joint, and might predispose these runners to injury.
Acknowledgment The authors would like to express appreciation for the support of the Fapesp [Project number = 2013/20400-3].
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