growthanddevelopment3347-blog

[growthanddevelopment3347-blog]

Introduction

Four female subjects were filmed and observed for this motor development analysis. They all fell within different developmental stages. The age in brackets indicates the age of the participant: - Early childhood (3 years old) - Later childhood (9 years old) - Adolescence (15 years old) - Older adulthood (80 years old)

Participants were given the instruction to "jump as high as you can", without further detail or specifics as to how they should jump.

The video camera was held at the height of subject’s centre of gravity, at a distance far back enough to ensure the subject would remain within the frame at peak height. One jump was filmed in the coronal plane and one was filmed in the sagittal. The video was arranged to play one view at full speed, followed by an edited version of the same jump from the same view at 0.125x speed.  

[growthanddevelopment3347-blog]

EARLY CHILDHOOD

The 3-year old in this video demonstrated many developmental characteristics of a child in the early stages of jumping. She performed several jumps in a row with the jump from front-view being the first. The side-view was a later trial after her confidence had increased with subsequent attempts.  

In the first jump, her elbows were flexed to 90 degrees and her arms were held in a winging posture with shoulders extended back. She held her arms stationary by her sides with no arm swing. Lack of arm movement is a clear indicator of early childhood jumping as it acts as a protective mechanism against falling. However, following the pattern of inconsistency in early motor performance, she increased her arm movement from the first video clip to the second (Focke, Strutzenberger, Jekauc, Worth, Woll, & Schwameder, 2013). In the second video, she started from the same flexed position, then extended her arms up during take-off in a semi-arm swing. Once airborne, she circled her arms to maintain for balance, abducting and extending her arms in an uncoordinated parachute motion (Haywood & Gretchell, 2009, p. 128). While landing, she flexed her elbows back to the starting position. This motor sequence is typical for children learning how to jump (Haywood & Gretchell, 2009, p. 126).

Her head and trunk were flexed forward for balance and she did not reach full extension at the peak of her jump. Proficient jumpers fully extend their bodies straight up to reach maximal vertical height (Haywood & Gretchell, 2009, p. 128) and this strategy was used by both the 9-year-old and the 15-year-old. Increased arm swing is a characteristic of an improved vertical jump (Floria & Harrison, 2013; Gerodimos, Zafeiridis, Perokos, Dipla, Manou, & Kellis, 2008) and is also a visible difference between this subject and the older, more proficient jumpers.

As is typical of most early skills, she had a very limited preparatory countermovement. At take-off, her feet left the ground at the same time. The two-foot symmetrical action demonstrated some progression of development (Haywood & Gretchell, 2009, p. 126). However, her knees stayed slightly flexed at take-off instead of extending fully. A proficient jumper would fully extend their legs for maximal vertical projection (Haywood & Gretchell, 2009, p. 128), as did the jumpers in later childhood and adolescence. Immediately after toe-off, her knees flexed further and stayed tucked under her body until she reached the peak of her jump. The lack of knee extension displayed her lack of proficiency (Haywood & Gretchell, 2009, p. 128). Most of the distance off the ground is gained from the knee tuck, not muscular power. Her muscles are less developed and therefore provide less strength compared to the two older girls.

Upon landing, her feet landed symmetrically, but she had minimal knee, ankle, and hip flexion to absorb the force. More proficient jumpers would require greater flexion of joints when landing. However, her small mass and low jump height resulted in a much smaller ground reaction force and she required less cushioning.

Overall, she exhibited many typical characteristics of an early jumper. As well, the change in technique between the two jumps demonstrated the variability and inconsistency of early developmental stages of motor skills.

[growthanddevelopment3347-blog]

LATER CHILDHOOD

Sgro, F., Nicolosi, S. and Schembri, R. (2015) conducted a study where they assessed vertical jump developmental levels in children between 9 and 12 years old. The jumps were evaluated based on six criteria  developed by the Department of Education Western Australia. None of the children were categorized as "beginners". Rather, they fell within the "developing" or the "consolidating" developmental levels because they demonstrated the three focus criteria of: ankles, knees, and hip bend; arms swing behind body; and ankles, knees, and hip bend on landing. Those in the "consolidating" level displayed the additional three criteria: head up, trunk upright; legs forcefully extend; and arms swing forward and up in time with leg action. Although the developmental level had links to participant age, it was not entirely age-dependent (Sgro et al., 2015).

Our 9-year-old participant matches the developmental stage of her age category as outlined in the study by Sgro et al. (2015). Although she is on the younger end of the age range, her jump may be categorized as "consolidating", as she demonstrates all six criteria listed above. Keeping in mind that age is only related, and not directly correlated, to proficiency, it was nevertheless expected that she would display proficient jumping. As a competitive synchronized swimmer, part of her training involves plyometrics: fast jumping movements that focus on generating maximum forces in minimal time. As such, she has developed more efficient jumping patterns to maximize biomechanical efficiency and produce the most favourable task outcome – characteristic of motor development changes.

Children take advantage of using their arms during jumping in a different way than adults (Floria & Harrison, 2013). Arm action, in children, results in a higher maximal jump height because it leads them to have a greater take-off height: they have a have a higher centre of gravity at take-off, presumably because of greater leg extension (Floria & Harrison, 2013). Coordinated arm action and leg extension are important criteria that distinguish "consolidating" jumpers from "developing" ones (Sgro et al., 2015). The way in which our subject moves her arm indicate that arm action is part of her natural movement patterns, but it is possible that if instructed to swing her arms further up she may achieve an even greater height.  

Although jump height was not measured, it is safe to say that the 3-year-old child would have had a smaller jump height, and the 15-year-old adolescent would have had a higher jump height (Focke et al. 2013). In girls, jump height increases with age until around 12 years old (Focke et al., 2013). We are able to make a reasonable assumptive comparison between the three age groups because they are all female. While boys jump slightly higher than girls when under the age of 12, the height difference increases continuously after puberty because of higher leg lengths, more muscle mass, and a greater percentage of fast-twitch muscles (Focke et al., 2013).  

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ADOLESCENCE

This 15-year-old adolescent actively displays the characteristic traits of a proficient jumper. She takes a leading step as she approaches her jump to help her build momentum while simultaneously lowering her body position in a preparatory crouch. This crouched position with her knees and hips bent and flexed is a critical part of the stretch-shortening cycle, which will allow for elastic energy to be stored (Haywood & Gretchell, 2009, p. 127). The countermovement of the preparatory crouch is responsible for the greater height achieved, compared to the early childhood and older adulthood stages. (Bobbert, Gerritsen, Litjens, & Soest, 1996)

The short leap immediately preceding her jump causes her to hit the ground with force greater than bodyweight, which in turn causes an equal and opposite ground reaction force upwards, facilitating vertical lift.

Both feet leave the ground at same time, showcasing symmetrical and uniform proximal to distal movements of her lower extremities, including hip and knee extension, that allow for optimal vertical lift (Haywood & Gretchell, 2009, p. 128).  Plantar flexion and ankle extension are present, with the toes being the last to leave the ground. This forceful, full extension of the legs is important to generate maximum power and is one of the “consolidating” criteria outlined previously (Sgro et al., 2015).  

The participant displayed an arm swing, extending her hands above her head as she took off, thus shifting her centre of gravity upwards and increasing acceleration upwards to allow for increased vertical lift (Liardi, 2017).

Reasons for why this participant is such a proficient jumper can be explained by sporting experience.  As a volleyball player proper technique and maximum height are continually trained and reinforced.   She also has experience doing high jump and the skills of arm swing, countermovement, and increased range of motion are directly transferable to proficient jumping.

In comparison to early childhood and later childhood, the participant is at a higher development stage. She has increased strength and coordination associated with muscle growth and training, as well as a larger knowledge base of good jumping technique that enhances her physical proficiency (Haywood & Gretchell, 2009, p. 129).  Compared to the older adult, this subject does not suffer any debilitating knee or hip degradation that would act as a rate limiter on her jumping ability (Haywood & Gretchell, 2009, p. 129). As well, her greater range of motion and flexibility is beneficial in both force production (Bobbert et al, 1996) and shock absorption – again, optimizing her vertical jump performance.

[growthanddevelopment3347-blog]

OLDER ADULTHOOD

The 80-year-old participant demonstrated the expected vertical jump characteristics of older adulthood. While certain aspects of proficient jumping were present, other components had regressed to early developmental stages resembling early childhood jumping.

Her trunk stayed relatively upright throughout the jump and her base of support remained relatively narrow with toes pointing forward, indicating that her balance had not deteriorated significantly (Liardi, 2017). Arm movements were symmetrical and both feet left the ground at the same time, indicating some proficiency. Although range of motion was decreased, she used a preparatory crouch prior to the jump, directing force downwards to maximize vertical height. She also flexed her hips, knees and ankles upon landing to absorb the force. These proficient characteristics are comparable to those present in young adulthood.

Strength was a limiting factor in the participant’s ability to get airbourne. Compared to younger age groups, her height and speed were significantly impaired. After the age of 70, both the number and size of muscle fibres decrease and by the age of 80, 30% of muscle mass is lost (Liardi, 2017). This loss in muscle mass, specifically in the quadriceps, gluteus and hamstring muscles, is evident in her lack of strength to lift her body weight off the ground. There is also a loss in explosive force present in aging adults (Haguenauer, Legreneur, & Monteil, 2005), reflected by a longer duration in the push-off phase.

A loss in range of motion in hip and knee flexion during the preparatory crouch is also common in aging populations and limited her vertical height: she was unable to stretch her muscles optimally and allow her legs to apply maximal force at extension (Haywood, 2009, p.127). Proficient jumpers are able to fully extend their legs, with toes plantar-flexed at takeoff, to lift their bodies high off the ground, but this subject did not display that knee or ankle extension.

Arm movement was extremely limited. Although they were not in a guarded position, indicating sufficient balance (Haywood, 2009, p.127), they remained at her side with minimal contribution. Proficient jumpers are able to extend their arms backward and swing them overhead to increase upward momentum (Haywood, 2009) and the participant did not utilize either strategy, unable to raise her arms above her head. Arm swing improves vertical jump performance (Floria & Harrison, 2013; Gerodimos et al., 2008), and the participant’s lack of arm movement indicates a regression back to previous developmental stages of arm swinging during jumping (Haywood, 2009, p. 126),  thereby reducing her ability to gain vertical height.

This older adult demonstrated many proficient characteristics that had regressed due to aging factors, such as loss of strength and range of motion. As a result, her vertical jump performance was significantly worse compared to the  adolescent, most closely resembling the performance of  early childhood stage.

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Conclusion

All four motor development stages were well-represented by our four subjects. Their jump characteristics and strategies followed expected patterns of development, displaying the influence of age-related motor development, as well as that of different training backgrounds and experiences.

Age, sex, and activity level all influence jump performance (Focke et al., 2013), but because all four individuals were female, differences in jumping proficiency can be compared without having to account for gender differences. Without needing to quantitatively measure jump height, it is evident that jump height increased from early childhood to later childhood to adolescence, before declining in older adulthood. This finding aligns with results from Focke et al. (2013) that showed counter-movement jump height increasing until age 12. Focke et al.'s study (2013) also found that very active subjects jumped higher than participants that were principally sedentary, again, supporting our own observations. Activity level of the 15-year-old was greater than that of the 9-year-old, which in turn was greater than that of the 3-year-old. With increasing age, activity level decreases and the 80-year-old presumably engaged in low levels of activity. This would have amplified the influence of the individuals' age on their jump performance.

There also lies key differences in visible movement patterns between the four participants. A more advanced development stage is associated with larger ankle and knee flexion in the crouch phase prior to the jump (Wang & Huang, 2004). This greater range of motion initiates the stretch-shortening cycle characteristic of jump countermovement that will store elastic energy to produce greater height (Bobbert et al., 1996; Wang & Huang, 2004). The weaker jumpers, the 3-year-old and 80-year-old, had significantly reduced range of motion and this was reflected in their performance. The highest jumper, the 15-year-old, had the greatest knee flexion, which combined with her momentum, resulted in the best height.  

Arm swing is another critical component to efficient jumping technique (Gerodimos et al., 2008; Floria & Harrison, 2013)  associated with increased motor development (Floria & Harrison, 2013). Although the way in which adults and children take advantage of arm movement is different, it nevertheless increases flight height for both age groups (Floria & Harrison, 2013). The two more skilled jumpers, aged 9 and 15 years, both demonstrated deliberate use of their arms to help them achieve more height. The other two subjects did not. For both, arm swing would come secondary to greater range of motion in a preparatory crouch, and presumably would be included once that limitation was overcome.

The different jump technique of the 15-year-old is a result of her sport-specific training, reinforcing that proficiency is not only based on developmental level, but also on external factors and influences.

In general, all four subjects matched their respective expected development levels  and painted an accurate picture of typical developmental changes that occur with age for this specific skill.

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References

Bobbert, M. F., Gerritsen, K. G. M., Litjens, M. C. A. and Soest, A. J. V. (1996). Why is countermovement jump height greater than squat jump height? Medicine and Science in Sports and Exercise 28: 1402-1412. 

Floria, P. and Harrison, A. J. (2013). The effect of arm action on the vertical jump performance in children and adult females. Journal of Applied Biomechanics 29: 655-661.

Focke, A., Strutzenberger, G., Jekauc, D., Worth, A., Woll, A. and Schwameder H. (2013). Effects of age, sex and activity level on counter-movement jump performance in children and adolescents. European Journal of Sport Science 13: 518-526.

Gerodimos, V., Zafeiridis, A., Perkos, S., Dipla, K., Manou, V. and Kellis, S. (2008). The contribution of stretch-shortening cycle and arm-swing to vertical jumping performance in children, adolescents, and adult basketball players. Pediatric Exercise Science 20: 379-389.

Haguenauer, M., Legreneur, P., Monteil, K. (2005). Vertical Jump Reorganization with aging: a kinematic comparison between young and elderly men. Journal of Applied Biomechanics. 21: 236-246.

Haywood, K. and Getchell, N. (2009). Life Span Motor Development (5th ed.). Champaign, IL: Human Kinetics.

Liardi, V. (2017). A Survey of Physical Growth and Motor Development. Personal Collection of V. Liardi, Western University, London, ON.

Sgro, F., Nicolosi, S. and Schembri, R. (2015). Assessing vertical jump developmental levels in childhood using a low-cost motion capture approach. Perceptual & Motor Skills: Physical Development & Measurement 120: 642-658.