Introduction
40 million Americans run regularly.1 Contrary to many runner’s beliefs, increased strength may be beneficial while not adding body mass. An increase in strength in specific muscles may improve running gait and performance. 9,6 Strength training may also play an important role in preventing common overuse injuries in running 11,12 Depending on the style of strength training, it may also have an enhanced benefit on running economy.4,16
Participation in CrossFit is also widely popular, with an increase in participation of 923% in the past ten years.2 CrossFit is a type of strength training in which most movements performed utilize the hip to generate a majority of the power for successful completion.8 Muscles of the hip and knee are imperative during many CrossFit movements, but also during running.
Purpose
The purpose of this study is to investigate the influence that CrossFit training has on running mechanics.
Methods
18 recreational runners between the ages of 18-65 were recruited in each of two groups: 9 runners that also participate in CrossFit 3 times per week, and 9 runners that do not do any strength training. Inclusion criteria included running at least 10 miles a week. Participants gave written consent and completed a demographic questionnaire and Physical Activity Readiness Questionnaire. Following consent, InBody (570, InBody USA, Cerritos, CA) bioelectric impedance body composition was collected.
Participants then completed a 5-minute treadmill warm-up. Retro-reflective markers were placed bilaterally on the shoulders and hips and unilaterally on the leg and foot. Data collection was completed over ground along a 10-meter runway with three embedded force platforms (1000 Hz, AMTI Optima, Watertown, MA). Preferred running velocity was then determined. Participants performed two separate conditions; preferred running velocity (C1) and a set velocity of 3.5 m/s (C2). Trials were collected via three-dimensional motion capture system (200 Hz, Vicon, MX and Vantage, Oxfordshire, UK) and photoelectric timing gates. Eight successful trials were collected for each condition.
Participants then performed strength testing of the hip and knee to determine peak torque using the isokinetic dynamometer (Biodex System 3, Biodex Medical Systems Shirley, NY) each consisting of one set of five reps at 120 °/s .
Data Analysis
Following collection, trials were individually processed using Vicon Nexus software (version 2.2.3, Oxfrodshire, UK). Trials were then exported to Visual 3D (version 5, Germantown, MD) and further processed.
Statistics
Kinematic and kinetic variables were analyzed with a 2x2 repeated measures ANOVA. Strength variables were analyzed with independent t-tests. Alpha level was set to 0.05.
Results
There was a significant difference between the CF group and the RO group in all of the strength measures, with the CF group having greater strength. For hip ROM, there were no significant differences between the groups, but there was a significant difference between the conditions.
Discussion
Although there were few differences between the two groups, the main finding of this study is that the CrossFit group was significantly stronger than the run-only group. This is of importance because it demonstrates that even though the CrossFit group was stronger, the running mechanics of the two groups were similar
