Laboratory 6

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Utah State University *

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4200

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Computer Science

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Dec 6, 2023

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1 Laboratory 6 Assignment Ground Reaction Forces • To gain practice in computing ground reaction forces. We apply force to the ground during every step we take. According to Newton’s 3rd law of motion (action-reaction), the ground applies equal and opposite forces against us during those steps. Force platforms quantify this ground reaction force (GRF) and, more specifically, allow us to quantify three components of the GRF: 1. vertical direction 2. anterior-posterior direction (forward-backward) 3. medial-lateral direction (side-to-side) Radin and co-workers (Radin et al., J. Ortho. Res., 1991, 9, 398-405) identified several biomechanical differences between a group of individuals that experienced mild, activity- related knee pain and a group that was asymptomatic (i.e., no symptoms of knee pain). One specific difference was that the knee pain group applied the vertical GRF more quickly at heel strike. Introduction and Objectives Force (N) Time (s) 1 2 3 4 Figure 1. Heel- Strike Toe-Off slope

2 The “heel - strike transient” is identified as the initial rise of the vertical GRF to a distinct peak or a sharp discontinuity (see point 1 on Figure 1). How quickly that component of the GRF rises is indicated by the slope of the heel-strike transient on Figure 1. None Purpose The purpose of this lab is to compare characteristics of the vertical GRF for two conditions: 1. walking with shoes 2. walking without shoes (barefoot or with socks) Procedure One student from each pair will walk across the force platform for each condition. Students should walk across the force platform with a normal walking speed and gait. Analysis 1. View each of the following points on each force trace. a. Heel-strike transient force (1). b. Impact peak (2). c. Minimum force at mid-stance (3). d. Active peak (4). 2. Fill out the following table for each condition (this has been done for you). a. Record the vertical distance to the following points on your trace to place in the N columns. b. Divide N by your body weight (BW) in newton ’ s to fill out the BW column. Body Weight (lb) x 4.45 N/lb = ___ 535 N _____ Without Shoes Condition With Shoes Condition Point N BW N BW 1 240 .45 250 .47 2 565 1.06 590 1.10 3 410 .77 400 .75 Equipment Needed

3 Without Shoes Condition With Shoes Condition 4 575 1.07 560 1.05 4. Measure the horizontal distance from the point of heel-strike to the point of the heel-strike transient along the time axis (x axis) of each force trace. Determine the time for each condition by using the formula below (record to four decimal places). Without Shoes Condition t = __.01 sec ________ With Shoes Condition t = __.05 sec __________ 5. Divide the heel-strike transient force in BW (point one) by the time you determined from number 4 to find the rate of the heel-strike transient force for each condition. Heel-Strike Transient Force Time Without Shoes Condition .45/.01= 45 BW/s With Shoes Condition .47/.05= 9.4 BW/s LAB QUESTIONS: 1.) Compare the time taken from the point of heel-strike to the point of the heel-strike transient between the conditions of without shoes and with shoes. What does the time for the “with shoes condition” tell us in comparison to without shoes? Looking at the two different variables we see that the heel-strike transient without shoes is 0.01 seconds. While with shoes the heel-strike transient is slightly longer, 0.05 seconds. This tells us that the transient force with shoes takes longer and is more gradual in spreading out the impact force when compared to without shoes. When walking without shoes it implies that the direct impact happens very quickly. 2.) Compare the 2 maximal forces (point 2 and 4) between each condition (with & without shoes). Briefly comment on any similarities and/or differences (time, slope, etc). When looking at the impact peak (point 2) and the active peak (point 4) when walking with or without shoes, it shows a few similarities and differences between the two. At the impact peak, it is slightly = Measured distance (mm) x one second (s) Measured distance for one s (mm) =

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4 higher with shoes (590 N) than without shoes (565 N). That means when wearing shoes, we experience an increased force during the impact compared to without shoes. But when we bring body weight into the equation, we can see that without shoes, the force per body weight is slightly higher. The active peak force is slightly higher without shoes (575 N) than with shoes (560 N). The time for the active peak is slightly longer with shoes, which makes walking smoother and more controlled. 3.) How is it possible that the force can be over 535 N (regular body weight standing) on the traces? There are other dynamic activities that go into walking like acceleration, deceleration, and how kinetic energy is transferred. These different dynamic activities combined with the individual's body weight give us higher forces than body weight (535 N). 4.) How can you apply these findings to athletic training or recreational runners? It can help us tailor training programs more specific to the individual based on their distribution of force and what kind of footwear they use. This can help improve their stride and how well they can apply force to give them more power with each step. It can also help with preventing injuries due to high impact. We can see what shoes they respond well to and what one’s help reduce the most amount of force impact with each step. 5.) Radin et. al. (1991) found the following heel-strike transient rates: Knee-pain Group = 68 BW/s Normal Group = 48 BW/s Compare our findings with Radin et. al. (1991). What is the ‘take home message’ of this lab? Comparing our finding to the Radin study we can see that our direct impact is significantly lower than those analyzed during the study. Our findings in the study with shoes show that the heel-strike transient rate is 9.4 BW/s and without shoes the rate is 45 BW/s. In contrast to the Radin study both of our rates are actually substantially lower than both the knee-pain Group of 68 BW/s and the normal group of 48 BW/s. The 'take home message' of this lab is that our choice in footwear has a significant impact on the heel-strike rate with each step. We can see that individuals with knee pain could greatly benefit from their choice in footwear. This can help reduce the amount of force they experience and reduce the amount of pain felt by the individual.

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