PhD A.I. Golovachev1
Dr.Biol. T.F. Abramova1
Dr.Biol., PhD B.A. Dyshko2
PhD S.V. Shirokova1
1All-Russian Research Institute for Physical Culture and Sport, Moscow
2LLC "Sport Technology" Association of Sports Engineering, Moscow
3Moscow Secondary Special School of Olympic Reserve #2, Moscomsport, Moscow
Keywords: sport ontogenesis, growth rate, explosive strength of lower limbs, maximal push-off force, maximal push-off time, force gradient, cross-country skier.
Background. Explosive strength of lower limbs is ranked among the key distance speed generation elements since it secures the horizontal propulsive force vector of the movement [5-6]. It should be mentioned, however, that the age- and sport-ontogenesis-specific strength and speed building components in the explosive strength development training systems are the most important and at the same time the least explored issues of the sport science [4, 7].
Objective of the study was to test and analyze the age- and sport-ontogenesis-specific strength and speed building components of the explosive strength (including the maximal push-off force and its timing) development training systems.
Methods and structure of the study. Sampled for the study were the 11-28 year-old male cross-country skiers (n= 696) (split up into four age groups) with the sport records of 3 to 20 years, qualified Class II to HMS. We applied the latest version of computerized dynamometric PD-3A test platform (made by Visti Co., Russia) to test the maximal push-off force, time and force gradient in the two-legs standing jumps with the knee bends of 120о to mimic the push-off phase of the classical diagonal ski stride. Test signals generated by the computerized PD-3A test platform were fixed, processed and analyzed by a special application LabView software toolkit to produce the following test rates: maximal push-off (ground response) force (Fmax), maximal push-off time (Tmax) and the force gradient (Jabs= Fmax/ Tmax), with the latter value assumed to fairly rate the explosive strength [1-3].
Results and discussion. The study found that the maximal push-off force rates (Fmax) significantly grow from 572±57 N to 1224±205 N (by 114.0%) in the age group of 11-12 to 19-22 years to reach a stable level. The next stabilization period in the period of 23-24 years comes to the peaking value of 1304±227 N (6.5%); and the 25-28 age group is tested with a gradual fall of these values to the minimum of 1138±121 N (-12.7% to the maximum) by 27 years of age followed by a little growth to 1168±141 N (-10,4%) by 28 years of age to stabilize at the levels typical for the 19-22 year-olds: see Figure 1, the top curve.
Figure 1. Maximal push-off force (Fmax) variation profiles with yearly increments by the age groups of 11-28 year-old cross-country skiers
Maximal push-off force (Fmax) growth rates were tested in the 11-12 to 13-14 years-old group (Δ13-14 – 11-12 = 289 N; 50,6%; tcomputed =6.354; р<0.001), in the pre-pubertal and pubertal active body growth phases. It should be noted that the fast growth rates (18.2% and 13.8%, respectively) are also typical for the pubertal 13-14 to 15-16 and 15-16 to 17-18 age groups followed by some stabilization; and then the yearly growth increments fall in the periods of 17-18 to 19-22 and 19-22 to 23 years of age (by 5.7% and 6.5%, respectively). The next growth (yearly incremental) period of 24 to 28 years was tested with further falls from -9.1% to -2.6% i.e. the maximal push-off force reduction with age.
The age-specific maximal push-off time (Tmax) variation profile showed no statistically significant differences in the yearly increments from the early to late pubertal phases: see Figure 2, the top curve. The maximal push-off time was tested to reduce in the period of 11-12 to 19-22 years from 0.40±0.03 s to 0.36±0.05 s (-10.0%) to reach a stable level. The next maximal push-off time (Tmax) reduction period at 23 years of age was tested to come to the first peak of 0.35±0.05 s (-2.8%) associated with the maximal push-off force peak: see Figures 1 and 2, the top curves. By 24 years, the push-off time was tested to grow (i.e. the push-off speed slowed down) to 0.36±0.05 s (2.9%) followed by a further sag in the period of 25 to 26 years to reach the second peak of 0.33±0.7 s (-8.3%). The age period of 26 to 28 years was tested with the further push-off time growth to 0.36±0.04 с (9.1%) coming to a stable level: see Figure 2, the top curve.
As far as the variations of the yearly increments of the maximal push-off times are concerned, they were tested to come to the maximums by the age of 19-22 years and reach a stable level (-5.3%); followed by the further push-off time sag by 24 years of age; and a new peak by 25 years (-5.6%).
Figure 2. Maximal push-off force time (Tmax) variation profiles with yearly increments by the age groups of 11-28 year-old cross-country skiers
In the age period of 26 to 28 years the skiers were tested with a stable increase of the maximal push-off time (reduction of the push-off speed), with the yearly increments varying from -2.9% to -5.9%: see Figure 3, the bottom curve. The age-specific maximal push-off time test data give the grounds to believe that this physical ability may be viewed as a compensatory mechanism activated in response to the maximal push-off reduction process in the age period of 24-26 years: see Figure 1, the top curve. The low Tmax growth rates in every age group may be indicative of this rate being genetically predetermined by the individual muscular performance patterns that may be provisionally referred to as the individual movement speed.
The age-specific variations of the force gradient appear to be determined, on the one hand, by the maximal push-off force to its time ratio and, on the other hand, by the neuromuscular coordination skills and control mechanisms maturing process: see Figure 3. The absolute force gradient was tested to meaningfully grow from 1447±249 N/s to 3500±980 N/s (by 141.9%) in the age period of 11-12 to 19-22 years to come to a stable level; with the first peak of 3826±1159 N/s (9.3% growth to the stable level) reached by 23-24 years of age – when the maximal push-off force comes to its life peak and with the shortest push-off time: see Figures 1 and 2, the top curves. In the age period of 25 to 26 years, irrespective of how low is the maximal push-off force with the shortening push-off time, the force gradient was tested to grow up to 4015.0±1410.0 N/s (by 4.9% to the prior peak). This period is followed by a further reduction of the force gradient to 3285.0±603.0 N/s (-18.2%) in the age period of 27-28 years due to the further fall of the maximal push-off force and grow of its time: see Figure 3, the top curve.
Figure 3. Explosive push-off force gradient (Jabs= Fmax/ Tmax) variation profiles with yearly increments by the age groups of the 11-28 years-old cross-country skiers
The highest yearly increment of the absolute force gradient (Jabs) was tested in the age period of 11-12 to 13-14 years (Δ13-14 – 11-12 = 844.0 N/s; 58.3%; tcomputed =4.657; р<0.001) i.e. in the active body growth phase. Later on, in the age periods of 13-14 to 15-16 years and 15-16 to 17-18 years (pubertal period) the growth rates were tested still high (17.8% and 16.9%, respectively) to come to stable levels; followed by the yearly increment reduction in the period of 17-18 to 19-22 years and 19-22 to 23 years – by 11.0% and 9.3%, respectively. The age period of 24 to 26 years was tested with the repeated yearly increment variation from -0.4% to 4.2%; followed by a regress of the yearly changes in the period of 27 to 28 years – within the range of -14.6% to -4.2%: see Figure 3, the bottom curve.
Conclusion. The maximal push-off (ground response) force (Fmax), maximal push-off time (Tmax) and the resultant force gradient (Jabs= Fmax/ Tmax) were tested to most actively progress in the age period of 11-12 to 19-22 years with a stable level attained with maturity, conditional on the reasonably efficient training system.
Peaks of the maximal push-off force and push-off time were found by 23 years of age versus the stable levels reached in the 19-22 year period – due to completion of the control mechanisms formation process. The above peaks are correlated with the body growth rates which slow down and stabilize by the age period of 19-22 years, with the growth peak achieved by 26 years of age. The progress is secured by the competitive requirements to the push-off speed, with the first peak of the force gradient achieved by 23 and the next peak by 26 years of age. The peaks of the push-off force gradients were tested being attained in the individually different age periods as determined by the genetic predispositions in the explosive lower-limb strength development process with the key role played by the strength component; plus more complicated and longer-achieved coordination skills to control the maximal push-off force and the genetically predetermined push-off time/ speed.
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The study analyzes the age-specific explosive strength rating test data including the maximal push-off (ground response) force (Fmax), maximal push-off force time (Tmax) and force gradient (Jabs= Fmax/ Tmax) in the cross-country skiers’ ontogenesis. The study found that the maximal push-off force, its time and force gradient normally grows in the period of 11 to 22 years of age in the pubertal to adult life period. The force progress peak point may be fixed when no statistically significant difference is found by the subsequent tests. It was found that since 23-28 years of age, in the early adulthood period, the maximal push-off strength of the lower limbs tend to sag with the further (albeit often statistically insignificant) drop in the push-off time to secure further growth of the force gradient that normally comes to its peak by 26 years of age. The 27-28+ year-old cross-country skiers were diagnosed with the maximal push-off force sagging and push-off time growth trends associated with falls in the force gradient.