Emily WeimerLaboratory EGround Reaction Forces in LocomotionIntroduction:The goal of this lab was for students to familiarize themselves with the similarities and differences that exist between walking and running ground reaction forces. In this lab, a force plate wasused to measure ground reaction forces, at two different speeds within each gait. By looking at two different speeds in each gait we are able to analyze the effects speed has within each form of gait. As previously discussed in lab, walking has a lower vertical displacement running, which results from lessstrides taking place during the same amount of time. When working with ground reaction forces, knowledge of Newton’s 3rd Law is essential. Newton’s 3rd Law states that every action has an equal and opposite reaction. Newton’s 3rd Law allows us to understand the equal and opposite reaction between the ground and the participant’s body on the force plate, which results from acceleration due to motion and gravity. Methods:In this lab, groups of students were instructed to work together at a single workstation, nominating one student to volunteer for all trials of walking and running speeds. To ensure data is obtained correctly, we set the frequency to 100 Hz, which records 100 samples per second. The participant will be asked to step on the force platform once during each phase of speed, slow walk, faster walk, slow run, and faster run. As the participant steps on the force platform it will determine theforces associated with the foot’s contact time during stance phase. The data should then be exported into an excel document to be interpreted. Results:2.65 2.85 3.05 3.25 3.45 3.65 3.850200400600800Vertical GRF - Slow Walking Time (s)Force (N) 2.8 2.9 3 3.1 3.2 3.3 3.4 3.5 3.602004006008001000Vertical GRF - Faster WalkingTime (s)Force (N)2.05 2.1 2.15 2.2 2.25 2.3 2.35 2.4 2.45 2.5040080012001600Vertical GRF - Slow RunningTime (s)Force (N)4.7 4.75 4.8 4.85 4.9 4.95 5 5.05040080012001600Vertical GRF - Faster RunningTime (s)Force (N)Gate Type & Speed Peak Ground Reaction ForceVertical (BW)Foot Contact Time (s)Slow walking814.1 N / 798 N =1.0202 BW3.78 – 2.80 =0.98 secondsFaster walking992.56 N / 798 N =1.2438 BW3.55 – 2.91 =0.64 secondsSlow running1516.74 N / 798 N =1.9007 BW2.44 – 2.12 =0.32 secondsFaster running1422.16 N / 798 N =1.7822 BW5.05 – 4.77 =0.28 secondsDiscussion:As expected, when moving at different speeds, the ground reaction force generated will also differ. In the walking gait, both slow and fast speeds exhibit similar graph trends, with the faster walk having a more significant slope for each trial because the ground reaction forces increase with the increased speed. The running gate should also follow this trend with the faster speed having a more significant slope but in our data that isn’t the case. This is most likely due to error on our end, maybe the participant didn’t fully step on the plate when doing the faster run, or because there was a lack of space, he started to slow down before reaching the plate so that he didn’t run into anything afterwards. The slow walk data appears to almost reach a plateau during one time period, but the faster walk dips down lower where the slow walk plateaus. The plateau indicates the period of time that the foot was fully on the force platform, which makes sense that the slow walk speed has it because the participantis moving at the slowest pace in that trial, meaning that the most time is spent on the plate then. Looking at the foot contact times can then back this up, with slow walking having a 0.34 second greater foot contact time. This is also seen in the running gait, with slow running having a 0.04 second greater foot contact time. The slow running foot contact time was about a third of the slow walking foot contact time. When participating in the running trials, the participant is traveling at a faster speed and will therefore experience an increase in stride frequency and an increase in horizontal velocity.The main reason for the difference between walking and running ground reaction forces is that during the walking gait, the mid-stance ground reaction force dips below body weight, which results ina negative acceleration, as the body is experiencing a heel strike. The running ground reaction force does the complete opposite at mid-stance, generating it’s peak force. Rather than somewhat plateauing like the walking data, the running data has a much more abrupt start and finish. There are relationshipsbetween the peak ground reaction force and the vertical displacement of center of mass that should also be noted. The two variables are directly related, meaning that as the vertical ground reaction force increases, the vertical displacement of COM also increases. As ground reaction force increases to its peak, the vertical displacement of COM will also be at it’s peak because the vertical displacement increases with the vertical ground reaction forces. The peak ground reaction force is greater in the running trials than the walking trials, indicating that the vertical displacement of COM was also greater during the running trials. As briefly discussed earlier, the running speed had a greater horizontal velocity which resulted in an increased stride frequency, which then results in a decrease in foot contact time. In both walking and running gaits, when the participant increased their speed, thus their horizontal velocity, the peak inthe graph is more significant and there is no period of plateau. As previously stated, our data does not show the trend that it should in regard to the running gait due to our error. The faster running speed should show an increased horizontal velocity, an increased stride frequency, a decreased foot contact time, and the greatest ground reaction forces. When comparing slow walking to fast running, the decrease in foot contact time results in an increase in the peak vertical ground reaction