Overcoming Gravity Book Review

[Gaetane Eary]

Aswe pulled out of a parking lot to caravan from the coffee shop to our shoot location, the phone slid across the dashboard in extreme slow motion. It was almost bullet time for me as I watched my iPhone slip free from contact with the car, inertia overcoming gravity and friction, the phone tumbling through air as my futile grab for it fell short.

Sure enough, the iPhone 6 woke up like nothing had happened. A bit of the weight lifted off my heart with that, but as I tried to operate the phone without cutting myself on the shattered glass, I was still a bit down.

STEM design! EGG-cellent! Students will use hands-on inquiry to find out more about gravity and how surface area can oppose it. Through trial and error based on collected data, students will design, create, and drop a vehicle carrying precious "cargo" from a ten-foot ladder, using a parachute to ensure a safe landing. When completed, students should have a better understanding of how gravity interacts with falling objects and how the surface area of a parachute can oppose those interactions.

This STEM challenge will engage 3rd grade students in thinking about the ways that a drought can affect a region or nation and how to find a solution to this problem. Students will construct a pipeline to transport water from point A to point B while overcoming gravity and will measure the volume of liquid before and after it travels through the pipeline. This STEM challenge combines architectural engineering with life science and mathematical measurement skills.

In this lesson, students will design and fly their own paper airplane and analyze their flight data to determine the best designs for getting planes to travel the farthest distance. Students will organize class flight data into a line plot and calculate the mean, median, mode, and range for the data set.

This Engineering Design Challenge is intended to help students apply the concept that gravity is a force that can be overcome from SC.3.E.5.4 as they build devices to "Stop the Drop." This challenge includes concepts beyond the benchmark.

Sprinting is a pure athletic endeavor of global appeal, with the 100 m race considered one of the blue-ribbon events at the Olympic Games. The 100 m Olympic final is broadcast worldwide to a potential audience of billions, and athletes from 83 different nations competed in the 100 m event (across both sexes) at the 2016 Olympic Games. At the start of any sprint event, sprinters commence from starting blocks, against which they must produce considerable acceleration. World-class 100 m sprinters can achieve around one-third of their maximum velocity in around only 5% of total race time by the instant they leave the blocks, and sprint start performance is strongly correlated with overall 100 m time (e.g., Baumann [1], Mero [2], Bezodis et al. [3]). Although a previous comprehensive review of sprint start biomechanics was published in this journal by Harland and Steele [4] in 1997, a wide range of descriptive, experimental and theoretical studies have since been undertaken. Many of these have used advanced technologies and methods to identify and understand several new important features of technique for sprint start performance. There is therefore a clear need to review the current understanding of the biomechanics of the track and field sprint start to provide current recommendations for both researchers and practitioners.

A schematic representation and definition of the events and associated phases during the sprint start, described using the terminology applied consistently throughout this review. The positions of the images are scaled for both horizontal displacement (horizontally) and time (vertically). Event timings are based on data from world-class male athletes during competition [27, 122] aside from the relative timing of rear block exit [3]

Total time taken is clearly the default, and appropriate, performance measure during an entire sprint. However, objectively defining successful performance during a discrete section such as the start is less straightforward. For example, does reaching a specific short distance (e.g., 5 m) earlier, or reaching this distance slightly later but with a greater instantaneous velocity, represent superior performance? This issue explains why many different performance measures have been used (Table 1) and why some experimental studies have reported apparently conflicting conclusions when multiple performance measures are considered [5,6,7].

The most common measure of sprint start performance has been center of mass (CM) velocity at block exit (i.e., block velocity; Table 1). Block velocity is determined by push phase impulse and can therefore be increased by either greater force or greater time spent producing force. The ability to produce force is not consistent throughout the duration of (and range of motion covered during) the push against the blocks. Therefore, there comes a point when attempting to achieve further increases in block velocity by simply pushing for longer against the blocks may not be beneficial for overall sprint performance (i.e., the least possible time to cover a given distance). In an attempt to overcome this limitation, average external power production has been proposed as an objective performance measure during any part of the start [5]. Average external power, which is typically calculated based on horizontal motion and normalized to participant characteristics, provides a single measure that accounts for the change in velocity and the time taken to achieve this change (i.e., the rate of change in kinetic energy) [5]. This performance measure has since been adopted in numerous sprint start studies (Table 1) and during early and mid-acceleration [8, 9].

Sprinters can choose the location and inclination of two foot plates in a block start [10]. Although three-point or standing starts are of interest for relay events and athletes in other sports, performance during standing starts differs from that out of blocks [11], as do the techniques adopted by sprinters and team sports athletes from their respective starts [12]. Our review therefore focuses on studies of sprint-trained athletes starting from blocks.

Wider medio-lateral foot plate spacings (0.45 m) affect hip joint kinematics (particularly non-sagittal) compared with typically used block widths (0.25 m), but do not affect block power [20]. Although the International Association of Athletics Federations (IAAF) does not specify limits to block width [10], given that sprinters are required to use starting blocks provided by the organizers in competition, that no manufacturer currently makes medio-laterally adjustable blocks, and that there appears to be no performance benefit of adjusting the medio-lateral spacing [20], there is limited need for further exploration in this area.

Whilst muscle excitation can vary considerably between individuals [25], it typically commences prior to horizontal force production against the blocks [25, 38], and the earlier onset of muscle excitation relative to the onset of force production has been positively correlated with maximal horizontal block force and block velocity magnitudes [25]. The rear leg gluteus maximus is typically the first muscle excited during the block phase [25, 52], followed by the rear leg semitendinosus [61] and biceps femoris, and then the quadriceps and calf muscles [25, 51]. The rear leg quadriceps are typically only excited during the early part of the rear leg push; excitation ceases prior to rear block exit to keep this foot clear of the track during the subsequent rear leg swing [51, 52], which may explain the sequencing of peak angular velocities in the rear leg. Whilst the vastii muscles are relatively highly excited during the rear leg push, rectus femoris excitation is less evident [61], which could be due to the importance of rear hip extension during this phase. Towards rear block exit, only the biceps femoris and calf muscles remain excited [51], which is consistent with knee extension being arrested but hip extension and ankle plantarflexion continuing.

After exiting the blocks, the first stance phase contains the greatest velocity increase during any stance within a maximal sprint [8]. Importantly, achieving high levels of block power is not associated with any potentially detrimental features of technique at first stance touchdown [3], and thus striving to improve push phase performance does not appear to inhibit subsequent technique.

Although long contact times are not desirable at maximum velocity, shorter block exit flight times and longer first stance contact times would increase the time during which propulsive force can be generated in this period of high acceleration and reduce the time spent in flight where force cannot be generated. Shorter flight times and longer contact times are also observed in higher-level sprinters in the step immediately after first stance toe-off [27], and this strategy may continue until mid-acceleration where rates of reduction in contact time become associated with performance [65]. However, caution must be applied since simply spending longer in stance to produce the same average force may not be beneficial due to the least possible time nature of sprint performance. As faster trials within session and within individual are associated with shorter contact times from the first step onwards [66], the longer contact times of higher-level sprinters are likely more related to longer-term physical adaptations, which facilitate this technical strategy. Coaches must therefore be cognizant of the trade-off between contact time and increases in velocity (i.e., net horizontal impulse) when exploring this.

At first touchdown, higher performing sprinters typically land with their CM further along the track [24]. The foot is behind the CM at first touchdown (i.e., a negative touchdown distance [3, 9, 26]), and moves progressively forwards relative to the CM at touchdown as a sprint progresses (e.g., by 0.09 m from touchdown one to two, and a further 0.09 m from touchdown two to three [26]). Irrespective of which point on the foot is measured, the CM is behind the stance foot from the third touchdown onwards [9, 26]. Whilst touchdown distance has been related to braking impulse magnitude during the early part of stance in the mid-acceleration phase (16 m) in athletic males [67], the link between touchdown kinematics and ground reaction force features during early acceleration remains poorly understood. This may be because a curvilinear relationship between touchdown distance and stance phase power likely exists [68]. This is due to an inability to produce sufficient magnitude of resultant force with the foot further behind the CM and an inability to direct this force in the required horizontal direction with the foot less far behind the CM [68, 69].

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