jumpsquat3347-blog

[jumpsquat3347-blog]

Introduction

     The jump squat is a modified vertical jump where an individual lowers their body into a squat before propelling themselves into the air. The nature of the jump squat requires a nearly simultaneous pattern of lower extremity extension to be able to lift and project the mass of the body upwards off the ground (Wang, Lin, Huang, & Yang, 2002). The phases of the jump squat are the following: 

1.   The preparatory phase is when the individual starts in a standing position and by flexing the hips, knees and ankles descends into a squat position.

2.   The flight phase is when the individual uses the energy generated from the squat to extend their knees and hips upward, propelling their body into the air.

3.    The landing phase is signified when the feet contact the ground again.

    In the jump squat, the lower limbs produce the mechanical energy to push the individual into the air (Satpathy, 2015). The quality of the squat performed will depend on the motor and cognitive development of the individual executing the action. “Motor control refers to the nervous system's control of the muscles that permits skilled and coordinated movements” (Haywood & Getchell, 2014). The level of control is correlated with the development of the nervous system and the strength of the skeletal muscle. The lifespan perspective explains how “important changes happen throughout the entire human lifespan” (Boyd, 2017, 1.4, Contemporary Motor Development, para 3). Infants and young children have weaker muscles and less developed bodily systems. Their body will grow and develop reaching its strongest and most developed form in early and middle adulthood. As one ages, however, strength and cognitive processes decline.

     It is hypothesized that there will be an improvement shown in the proficiency of the jump squat throughout the age groups, with the best performance during adolescence and a sharp decline in performance during older adulthood. These changes throughout the lifespan are shown in the execution of the jump squat done by various age groups. Each age group shows a variation in the overall form, balance, and understanding of the movement.

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Early Childhood (2-6)

     Nathan is a 5-year-old child with limited knowledge and experience performing a jump squat. The video depicts accurate movements of what is to be expected from early childhood. Brain growth, synapse formation, and myelinization continue in early childhood which contributes to the increased synaptic speed and reduced reaction time for many basic motor movements (Boyd, 2017, 7.2, The Brain and Nervous System, para. 1). By 2 years old, an individual’s gait becomes smoother and more rhythmic as it is secure enough to start jumping (Berk, 2012). By the age of 4 or 5, a child can use a smooth, flexible motion involving the shoulders, torso, trunk, and legs as upper and lower body skills combine into more effective actions (Berk, 2012). The task of the jump squat is more complex due to the technical aspects of the proper squatting movement that may be unfamiliar during early childhood.

     The primary challenge during the jump squat for the child is being able to generate enough leg strength to propel the body off the ground (Wang, 2002). This is due to the musculoskeletal system not being fully developed in early childhood (Berk, 2012). Specifically, there is a smaller percentage of type-II motor-unit utilization during early childhood that compromises a child’s muscle function in a task such as a jump squat (Falk et al., 2009).

     During the preparatory phase, it is evident that Nathan’s balance is not secure as his feet are not shoulder-width apart and are too close together. When Nathan attempts to squat down to optimize the force generated in the preparatory phase, his body alignment is angled with his body flexed at the hips and his chest facing towards the ground. This body alignment biomechanically affects the optimal angle in the hips, knees, and ankles to project the individual vertically during the jump squat movement (Wang, 2002). The biomechanics of Nathan’s movement infers that his musculoskeletal system has not been fully developed and matured to the extent where his muscles can support the proper technique.

     The video depicts the child having difficulty squatting lower in the preparatory phase. This leads to a lower vertical jump due to the decreased amount of force generated for the flight phase once Nathan is airborne. Notably, a decreased amount of force generated is also due to the lower motor-unit activation in boys than in men for the knee extensors, which help generate enough force to lift the body off the ground (Blimkie, 1989). In addition, children will have lower skills in terms of the range of motion in the hip, knee and ankle joints that leads to limited flexion to get lower during squatting movement in the preparatory phase (Wang, 2002).

     As Nathan’s feet touch the ground during the landing phase, he does not land softly on the balls of his feet, but rather flat-footed in a discontinuous motion with an abrupt pause before entering back into a squat. A proficient jump squat would have the individual continuously land on the ground and enter the squatting movement fluidly. In addition, Nathan lands each jump with his feet staggered or wider than how they were during the preparatory phase to shift his center of gravity so he is more balanced during the movement. In contrast, 18-year old James is able to remain stable and balanced during the landing phase through the simultaneous flexion in his hips, knees and ankle joints to absorb the impact of the landing.

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Middle Childhood (6-12) 

     Alex is a 12-year-old boy who has never done a jump squat before.  When watching him perform the movement it is evident that he has not reached his maximum strength and balance, and he lacks fluidity in the movement.

     In the preparatory phase, as Alex squats down it is evident that his balance is not secure and that he lacks strength in his legs. As he lowers his body down, he shifts his weight onto the balls of his feet, transferring his center of gravity forward. During this movement he also everts his feet and his knees collapse inward. Dotan et al. (2012) explains how there is, “lower motor-unit activation in boys than in men in the knee extensors.” With less activation of the muscle, it is more difficult to keep lower limb alignment. When Alex bends his knees, instead of activating his gluteus maximus, he folds his upper body forward and down. It can be inferred that as Alex is able to squat deeper than Nathan he has more strength in his lower limbs. However, he still lacks the joint stability and is unable to keep his body in proper alignment the way James does when he performs the movement.

     In the flight phase, Alex extends his knees and propels himself into the air. When he attempts this movement, there is lack of fluidity. In a perfect jump squat, one would use the power generated from the squat to propel them directly into the air, as shown when James performs the movement. Alex, however, stands up slightly from his squat position, pauses, and then jumps, preventing the ability for him to use his maximum power.

     The landing phase is signified when his feet touch the ground again. Ultimately, as one’s feet touch the ground, their knees would simultaneously begin to bend to allow for a continuous motion. However, when Alex’s feet land back on the ground he has to rebalance himself interrupting the flow of the movement. Coordination is best developed between the ages of 10-13 (Grasso, 2018). Seeing that Alex is 11, he posses the coordination skills to carry out the action but has not mastered this skill, causing a lack in fluidity. After performing the jump a few times in a row he begins to lose his balance on landing. “Balance is maintained through a complex process involving sensory detection of body motions, integration of sensorimotor information within the central nervous system, and execution of appropriate musculoskeletal responses” (Bok, Lee, & Lee, 2013). Middle childhood is a period of significant synaptic pruning and cognitive growth. By this time, the brain is significantly more developed than in early childhood. However, there is still a large amount of development and maturation to come. As a result, Alex is able to stay relatively more balanced than the young child performing the jump but still wobbles on landing, showing he has not fully developed these functions.  

     “Brain growth in the frontal lobes of the cerebral cortex becomes the focus of development processes later on in middle childhood” (Boyd, 2017, 9.2, The Brain and Nervous System, para. 2). The frontal lobe is responsible for executive processes and is developing during middle childhood. In the jump squat one must be planning and adjusting each future movement while executing the current aspect of the movement. As a result, Alex is better at thinking ahead and planning the next step of the movement compared to Nathan. However, the lack of fluidity demonstrates that he still needs to stop and think before he can execute the movement, demonstrating that the frontal lobe is not fully developed. 

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Adolescence (13-18)

     James is an athletic 18-year-old male who has experience performing jump squats. Due to this previous experience, he should be able to perform a jump squat with the highest level of skill compared to the other age groups. Boyd (2017), stated that, “a man's strength is at its peak during their early 20s to 30s as they tend to be more physically active during that time” (13.3, Strength and Speed, par. 6). Myelinization is also complete for motor movements and nearly complete for other areas of the brain by this age. This explains why James is able to complete the jump squat faster and is able to concentrate for longer, compared to the other age groups. The video of James differs however from the rest as he does not have a back view of the jump. This is because the myelinization for the reticular formation is not fully complete until an individual’s mid-20s meaning that James’ ability to focus is not as efficient as an adult (Boyd, 2017, 4.1, Myelinization, par. 9).

     During the preparatory phase, James is in a stable stance and is able to lower himself down into a squat in a controlled fashion. He is able to keep his center of gravity close to his midline allowing him to squat lower compared to the other age groups. Adolescent boys still have hip flexibilities similar to prepubertal boys (Zakas et al., 2002), which along with increased leg strength allows James to enter into a lower squat compared to the other age groups. James’ abdominal strength also allows him to remain balanced and in control of his movements. McBride et al. (2010) stated, that the depth of the squat affects the height of the jump as it controls the amount of power used to propel oneself into the flight phase.

     During the flight phase, James is able to push himself off the ground with more height and fluidity compared to the other age groups. Haguenauer, Legreneur, and Monteil (2005) explain that adolescents are able to use more explosive forces as well as a proximal-distal coordination pattern. This pattern allows for the body’s center of gravity to be in the correct place at takeoff, allowing for lower limbs to be fully extended and produce more power. Adolescents are also able to recruit all their motor neurons at once, allowing them to have more power compared to a child (Arabatzi et al., 2014). Power is a vital component in jumping as the more power one has, the more desirable their movement will be (Cormie, McBride & McCaulley, 2008). This explains why James is able to push himself higher off the ground and have the most desirable jump squat of all age groups.

     As James’ enters into the landing phase his knees begin to bend simultaneously with his feet touching the ground, allowing him to enter back into the preparatory phase. We can see in the video that James is able to remain stable and in control, not leaning too far to one side as he lands. Joint development allows adolescents to have coordination levels close to that of adults (Boyd, 2017, 11.2, The Skeletal System, par. 7). This allows James to continue to perform the movement multiple times with the same control, balance, and fluidity.

     Since James is 18 he is nearing his peak level of performance, which along with having performed this skill before results in a more automatic movement, requiring him to think less and perform the skill superiorly compared to that of the other age groups.

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Older Adulthood (60 +)

     Mal is an 89-year-old woman that likes going for 10-minute walks for exercise but generally is inactive. She has never done a jump squat before. Please note the duration of each video from the various sides are not the same duration as Mal became tired. During older adulthood, there is a general slowing down of both physical and cognitive functions. Within the brain and nervous system, there is a loss of dendritic density causing the gradual slowing of synaptic speed and therefore an increase in reaction time for many everyday tasks, reducing her ability to perform this new activity (Boyd, 2017, 17.6, General Slowing, para. 1).

     As shown in the video, in the preparatory phase there is a loss of dexterity as Mal uses her arms to propel herself upwards despite being directed to keep her arms extended forward. Her vision follows her arms displaying the inability to automatically accomplish the movement. Therefore, Mal is unable to control both actions at once. This probably due to deficits in cognitive function as she is an Alzheimer’s patient (Paula et al., 2016), and has arthritic changes in her joints (Boyd, 2017, 17.6, Motor Function, para. 1-3). Additionally, her knees are unable to fully flex eccentrically into a crouch indicating a loss of elasticity in her muscles. As she lowers her body, it is evident that her knees begin to wobble, and is unable to keep her upper body upright and naturally rounds her shoulders. This demonstrates the body’s overall loss of muscular strength (Borst, 2004). As a result of the poor muscular strength of the gluteus medius, soleus, and gastrocnemius, the older adult uses other muscles to compensate, swinging her arms for propulsion and using her back muscles (Borst, 2004).

     Subsequently, in the flight phase, there is a significant lack of power and explosive movement as the jump is lacking in height (Haguenaeur, Legreneur, & Monteil, 2005). This may be a result of a reduced ability to produce force because of the decrease in the linear velocity and angular amplitude of the hip, knee, and ankle. (Haguenauer et al., 2005). Mal instinctually lifts her arms upwards despite initially being directed to keep her arms extended in front of her body. This may indicate the loss of dexterity and inability to accomplish many gross motor functions at once which can be a consequence of the degeneration of higher level functioning (Scherder et al., 2007).

    Lastly, during the landing phase, there is a lack of continuity from the initial landing of Mal’s feet to the final lowering of the body into a squat, most likely due to the lack of balance and muscular strength (Borst, 2004). As the muscles are unable to maintain balance after the impact of the jump, she first regains balance before lowering her legs demonstrating a decrease in event detection and speed of postural adjustments (Izquierdo et al., 1999).  Her difficulty with balance may also be due to hippocampal degeneration that is common in those with Alzheimer’s, thereby causing gait and spatial orientation deficits (Scherder et al., 2007).  Additionally, as the exercise continues, her stamina diminishes as the movement becomes less precise and she begins to tip over, touching the floor to regain balance. Mal’s muscles can no longer sustain the movement.

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Conclusion

     Overall, each video displayed that the jump squat is distinct throughout each of the age groups. To begin, during early childhood the ability to execute the jump squat is challenging as a child’s musculoskeletal system is not fully developed resulting in decreased leg strength and coordination. This improves into middle childhood where the child is able to perform the movement to a better degree and for a longer duration. However, during middle childhood, an individual still lacks the strength, coordination, and fluidity to perform the movement multiple times. The execution becomes ideal in adolescence when the individual has reached their peak for strength and coordination, allowing them to move through the movement with control and fluidity not seen by the younger age groups. As an individual enters into later adulthood, their ability to execute the jump squat begins to deteriorate, due to a loss of strength and balance.

     The differences between the age groups executions of the jump squat are noticeable when looking at key factors such as coordination, balance, muscular strength of the lower body, power, and the fluidity from the jump to the squat. It is also interesting to note the similarities in early childhood and late adulthood where both Nathan and Mal had similar difficulties with balance, squat depth, and jump height. The two also lacked the smooth, fluid motion from the vertical jump to the squat. This shows that there may be a greater need to identify additional phases in order to distinguish better between the abilities of the oldest and youngest age groups. The cerebellum acts as the body’s movement and balance control center. The cerebellar volume peaks at age 15.6 years in males, which explains the lack of balance and stability during Nathan and Alex’s squat jumps (Bernard & Seidler, 2014). In addition, the volume of the cerebellum is smaller and white matter integrity is reduced in older adults explaining Mal’s difficulty performing the movement (Tiemeier et al.,2010).

      Our findings are consistent with our hypothesis as we assumed that motor performance would steadily increase and peak at adolescence, and then worsen during older adulthood as described in past research (Leverson, Haga & Sigmundsson, 2012). James was seen to perform the jump squat with the highest level of skill compared to Alex, Nathan, and Mal who were seen to have more difficulty. However, each of the individuals studied cannot be generalized to the external population for their age groups, as there are many variations within individuals at all ages.

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