WK 5 RESPONSES

1. I found the article very interesting. I would not have thought that the gastrocnemius played such an important role in hip joint angle. In my undergrad degree, I performed the sit and reach test for multiple classes. Every time though, our ankles were in a dorsiflexed position. After reading the article for this week, I am thinking that our ankles should have been relaxed, or plantarflexed, before attempting the test. This would have made a difference in the results of the test, plus it would have been a more accurate measurement of hamstring flexibility. The article also makes me think about how I perform a supine hamstring stretch for patients. I was taught that with the person supine, the leg is raised, knee kept straight, the ankle is dorsiflexed, and the whole leg is flexed toward the chest. Interestingly, when I am the one being stretched, I feel the stretch in my calf before I feel it in my hamstring, which is one thing that the article mentioned (Kawano et al., 2010). For years, I’ve thought that in order to get a “good” stretch, the entire posterior chain of the lower limb needed to be stretched. This article proves otherwise. The authors even say that for muscles that cross multiple joints, one joint has to be loose or relaxed in order to get the most stretch from the other muscle (Kawano et. al., 2010). Another thing that surprised me was how much greater the results were for the females in the study compared to the males. I assumed the women would have more flexibility, but I did not think it would be to the extent that it was.

2. Linear velocity of a point on a rotating body is “determined by the angular velocity of the rigid body and the distance from the axis of rotation to the point on the body” (Flanagan, 2019). When the angular velocity is increased the linear velocity is also increased. Also if the distance from the axis of rotation to the point on the body is increased the linear velocity will also increase. Because velocity can be modified, the angular velocity would be the easiest to control. Based on the equation v = l x w neither factor contributes to a greater impact. From a mechanical perspective, “because the two terms l and w are multiplied together, an increase in either one will increase the linear velocity by the same amount” (Flanagan, 2019)

3. When a body is in rotation, the angular velocity and length from the axis of rotation to the end of the body determine the linear velocity due to and tangential and centripetal forces placed on the body during rotation (Flanagan, 2019). In lesson five of the text, Flanagan (2019) uses hammer throwing the show how one can change the angle of the release to change the linear velocity and increase the distance of the throw.  Changing the length of the body from axis to end can increase linear velocity by tangential force, i.e. increasing the radius of a bicycle tire will likely increase the linear velocity of the bicycle (Flanagan, 2019). While on can control either of these variables, if the length of the body is fixed, then changing the angle would have the most impact, because it is the variable that can change consistently, regardless of the situation.  Like the lessons discussing projectile motion and linear velocity, the angle which one releases an object, like a ball or an Olympic hammer, will have a far greater impact on distance, which is usually angular kinematics means to an end (Flanagan, 2019).

4. The two ways linear velocity of a point on a rotating body can be increased is by (1) increasing the angular velocity of the body and (2) changing the distance from the axis of rotation to the point (Flanagan, 2019). Regarding which factors are controllable, both the angular velocity and the distance from the axis of rotation to the point can be controlled. The distance from the axis of rotation to the point on a rotating body is a fixed length and will remain constant throughout the entirety of an experiment. Varying distances can be examined when additional units, with various distances between axis of rotation and point, are introduced to an experiment. Angular velocity is not as reliable, especially when the velocity is produced by a human being versus a machine. The mathematical equation for linear velocity is v=lr*(omega) where lr is the distance between the axis of rotation and the point on the rotating body and omega is the angular velocity (Flanagan, 2019). This equation implies that an increase in lr or omega would also lead to an increase in the linear velocity. However, this is not always the case. Without going into too much detail, the lr term, when increased, may not always lead to an increase in linear velocity; this is due to the added difficulty to rotate the point around the axis of rotation due to an increase in size and mass (Flanagan, 2019). With that said, the angular rotation term (omega) would have the biggest impact since it is the easiest to quickly change and does not have adverse effects once increased past a certain point.

5. I’ll begin with my experience that I feel is relevant and interesting. I recall being in grade school and we always did the sit and reach test. The test was performed with a box at our feet and we were to push a sliding marker along a measuring stick. By stationing our feet against the box, it automatically put our ankles in plantar dorsiflexion. Many of us would try to project the marker as far as we could without actually experiencing the discomfort mentioned in the gastrocnemius noted in the article. We were never asked to hold our position but to push the slider as far forward as possible. By using this projection method, it’s extremely likely the results were inaccurate and invaluable to those giving the tests. When I went into Jr. High the chair sit and reach test was being offered as a substitute for the sit and reach test for those who felt the standard sit and reach may have been too painful. In addition, they got rid of the sliding marker and you were then asked to hold the position. What I still find quiet interesting is that when people are trying to increase the flexibility they have in their hamstring they will often stretch with their ankles in dorsiflexion so I don’t really understand how the original sit and reach test does not accurately measure the flexibility of that muscle. I’m not surprised that by eliminating the effect of the gastrocnemius, participants were able to gain better results. I was surprised to note that by eliminating the gastrocnemius the result was not impacted by height. I’m taller than most and always scored lower that my shorter friends on the standard sit and reach test. However, I was told by those administering the test, not to worry, I would score lower because I was taller. It sounds like this might be a better method to implement. 

APA Format

Due Saturday June 15, 2019