Download Knee Extensor Muscle Strength and Vertical Jumping Performance

Pediatric Exercise Science, 2001, 13, 60-69
O2001 Human Kinetics Publishers, Inc.
Knee Extensor Muscle Strength and
Vertical Jumping Performance Characteristics
in Pre- and Post-pubertal Boys
Mati Paasuke, Jaan Ereline, and Helena Gapeyeva
Knee extensor muscle strength and verticaljumping performance characteristics were compared between 14 pre-pubertal(1 l-year-old) and post-pubertal
(16-year-old) boys. Post-pubertal boys had greater (p < .05) absolute values of
maximal isometric force (MF) and rate of force development (RFD),absolute
and body mass-related values of isokinetic peak torque of the knee extensor
muscles at angular velocities of 60, 180, and 240" . s-', as well as jumping
height in squat, counter-movement, and drop jumps, than pre-pubertal boys.
This study indicated an inability to use the positive effect of stretch-shortening cycle to vertical jumping performance in pre- and post-pubertal boys.
Introduction
Maximal and explosive muscle strength (power) are important characteristics of
neuromuscular performance, which changes throughout the years of growth, particularly during puberty. Numerous studies in this field have focused on measuring
the maximal isometric or isokinetic strength, which gives information about the
maximal voluntary force-generating capacity of the muscle groups, and vertical
jumping performance, which provides information about the explosive force production (power output) of the leg extensor muscles by measuring jumping height.
The significant increase in maximal isometric strength (4, 15, 26) or isokinetic
peak torque at different angular velocities (9, 14, 26), as well as vertical jumping
height (1 1, 15) during puberty is well documented. However, a smaller number of
studies have assessed associations between maximal strength of the leg extensor
muscles and vertical jumping performance throughout puberty. Only a few studies
have reported the rate of voluntary isometric force development of the knee or leg
extensor muscles in pre- and post-pubertal children (1 1,15).
The increase in maximal strength of the muscles during puberty is often
associated with increase in muscle mass (18) or cross-sectional area (17). Some
investigations demonstrated a significant increase in muscle strength in relation to
The authors are with the Institute of Exercise Biology at the University of Tartu, 5
Jakobi Street, 51014 Tartu, Estonia.
60
Knee Extensor and Vertical Jumping -61
body mass between 8-year-old and 13-14-year-old children (9,26). However, the
studies that have used anthropometric measures (8) or ultrasonic techniques (16)
have reported that isometric strength expressed per unit of cross-sectional area of
the muscles would appear to remain unchanged throughout puberty. Thus, the differences in maximal isometric and isokinetic muscle strength in relation to body
mass in pre- and post-puberty need further recordings.
The knee extensor muscles play an importantrole in many movement activities. These muscles have a great importance in the function and stability of the
knee joint as well as prevention of the knee injuries.
The purpose of this study was to compare the isometric and isokinetic strength
of the knee extensor muscles and vertical jumping performance in pre- and postpubertal boys. More specifically, we were interested in exarning maximal isometric force and rate of force development as well as isokinetic peak torque of the
knee extensor muscles and jumping height in squat, counter movement, and drop
jumps in 11-year-old and 16-year-old boys. A squat jump consists of a concentric
muscle action of the leg extensor muscles, while counter-movement jump, drop
jump (i.e., jumping down from a height), and performing a maximal vertical jump
upon landing, consists of an eccentric-concentricmuscle action (stretch-shortening cycle). It has been shown to have a potentating effect of stretch-shortening
cycle to vertical jumping performance in young adult subjects (2,6); however, the
age-related differences of this potentating effect are poorly understood.
Material and Methods
Subjects
Twenty-eight boys, aged from 11 to 16 years, participated in this study. The subjects were distributed into two groups: pre-pubertal (11-year-old, n = 14) and postpubertal (16-year-old, n = 14) boys (Table 1). Pubertal stages were determined
according to the criteria of Tanner (27). All 11-year-old boys were in Tanner stage
1 and were classified prepubertal as to pubic hair and genitalia. Informed parental
consent was obtained prior to the children's participation in the experiment. All
16-year-oldboys were in Tanner 5 stage and were classified as post-pubertal. Their
written informed consent was obtained. The study carried the approval of the University Ethics Committee.
Table 1 The Physical Characteristics of the Subject Groups
Age groups
Variable
Pre-pubertal boys (n = 14)
--
.
Post-pubertal boys (n = 14)
--
Age (years)
Height (cm)
Body mass (kg)
11.4 fTI--152.8 k 2.9
40.3
+ 2.8
r6.4-ref-----176.5 1.7
+
67.8 f 2.5
Note. Variables are expressed as M f SE. All characteristics were significantly different ( p
< .05) among groups.
62 - Paasuke, Ereline, and Gapeyeva
Twenty-four to 48 hours before data collection, the subjects were given instructions and the strength testing procedures, and vertical jump tests were demonstrated.
This was followed by a practice session to familiarize the subjects with the procedures. The subject's dominant leg was determined based on a kicking preference.
Prior to testing, each subject underwent a 10-min warming-up period. Postpubertal boys performed 5-rnin submaximal ergometer cycling followed by stretch
exercises of knee extensor and plantarflexor muscles. Pre-pubertal boys performed
running and stretching exercises.
Isometric Dynamometry
During the measurement of maximal isometric force (MF) and rate of force development (RFD) of the knee extensor muscles, the subjects were seated in a specially designed dynamometric chair, with the knee and hip angles equal to 90" and
1lo0, respectively. The body position of the subjects was secured by three Velcro
belts placed over the chest, hip, and thigh. The isometric force of the knee extensor
muscles was recorded by standard strain-gauge transducer mounted inside a metal
frame that was placed around the distal part of the ankle of the dominant leg above
the malleoli using a Velcro belt. The electrical signals from the strain-gauge transducer were digitized online (sampling frequency, 1 kHz) using a personal computer. The digitized signals were stored on a hard disk for further analysis. During
the testing, the subject was instructed to react to the light signal (ignition of the
signal lamp, placed 1.5 m from the subject) as quickly and forcefully as possible
by extending the leg against a cuff fixed to a strain gauge system, maintaining the
maximal effort as long as the signal was on (2 s). Three attempts were canied out,
and the best result was used for further analysis. A rest period of 1 min was allowed between the attempts. The force-time curve and light signal were analyzed
by personal computer. Isometric MF and RFD as the force in relation to time period of 0.2 s from the onset of the force production were calculated.
lsokinetic Dynamometry
Isokinetic concentric peak torque (PT) of the knee extensor muscles was measured
using a Cybex I1 dynamometer and manual (Lumex, Ronkonkoma, NY). After
calibration of the dynamometer, subjects were seated in the adjustable chair with
support for the back and hips, and were stabilized via straps at the chest and thigh.
The axis of rotation of the knee joint was aligned with axis of the dynamometer
lever arm.The force pad was placed 3-4 cm superior to the medial malleolus, with
the foot in plantigrade position. The knee of the dominant leg was positioned at
90" of flexion. Range of motion during testing was set using the goniometer through
an arc from 90" of knee angle to full extension. Subjects were instructed to hold
their arms across the chest to further isolate knee joint extension movements. During the testing, the subjects were asked to produce knee extension as forcefully
and quickly as possible through a complete range of motion. Verbal encouragement was given during every trial. Three attempts were carried out at angular velocities of 60, 180, and 240" - s-', and the one with the highest PT value was used
for further analysis. The trial proceeded from the slow to the high angular velocity.
A rest period of 1 min was allowed before and between the attempts. All torque
measurements were gravity corrected.
Knee Extensor and Vertical Jumping -63
Vertical Jump Tests
The verticaljumping tests were performed on force platform (PD3A, VISTI, Russia) with the dimensions of 0.75 X 0.75 m and natural frequency of 150 Hz. Three
types of maximal verticaljumps were performed: squat jumps, counter-movement
jumps, and drop jumps. Squat jump (SJ) started from a static semi-squattingposition with a knee angle of 90" of the knee flexion, followed by subsequent action,
during which the leg and hip extensor muscles contracted concentrically. Countermovementjump (CMJ) started from upright standing position immediately after a
fast preparatory counter-movement that stretched the leg extensor muscles (eccentric contraction). This was followed by an explosive maximal extension in the
opposite direction (concentric contraction). The starting position during drop jump
(DJ) was similar to that of the CMJ, but the subject stood on a box of a dropping
height of 40 cm. The subject dropped from the box and rebounded after a short
contact with the ground for maximal height. The leg muscle work during the ground
contact constituted the stretch-shortening cycle. The subjects were instructed to
jump with their hands on the hips to eliminate the influence of the arm swing
impulse. The movement amplitude of the knee joint during each jump was measured with electrogoniometer(ELGON) attached to the lateral side of the subject's
right knee. Prior to the testing, the subjects performed several preliminary trials.
The flight time was used to calculate the jumping height by the height of rise of the
center of gravity of the body above the ground (2). Each jump was repeated three
times, and the best result was used for further analysis. A rest period of 1 min was
allowed between the jumps.
Statistical Analysis
Data are means and standard errors of mean. One-way analysis of variance
(ANOVA) following by Tukey post hoc comparisons were used to test for differences between age groups and for each vertical jumping exercises. A level of p <
.05 was selected to indicate statistical significance.
Results
-
Post-pubertal boys had higher (p < .05) height, body mass, and body mass index
than pre-pubertal boys (Table 1). Isometric MF and RFD of the knee extensor
muscles were greater (p < .001) in post-pubertal boys compared with pre-pubertal
boys (Figure 1). However, no significant differences ( p > .05) were observed in
isometric MF and RFD of the knee extensor muscles in relation to body mass
between the groups. As shown in Figure 2, post-pubertal boys had greater (p < .05)
absolute
and body mass-related isokinetic PT of the knee extensor muscles at an- gular veibcifie~of60;180, and 2 W . s-' c
o
~
~
t
t
m
ing height in SJ, CMJ, and DJ was higher (p < .05) in post-pubertal boys than prepubertal boys (Figure 3). No significant differences in jumping height between SJ,
CMJ, and DJ were observed, either in pre-pubertal or post-pubertal boys.
p
-
64 - Paasuke, Ereline, and Gapeyeva
-
Figure 1 Mean (BE)
maximal isometric force (MF) of the knee extensor muscles
and MF force relative to body mass (A), rate of isometric force development (RFD) of
the knee extensor muscles, and RFD relative to body mass (B) in pre- and post-pubertal boys. ***p < -001.
Discussion
This study indicated markedly greater isometric MF (36.6%) and isokinetic PT of
the knee extensor muscles at low, medium, and high angular velocity (54.5%, 52.4%,
and 54%, respectively) in post-pubertal boys compared with pre-pubertal boys.
The increase in absolute values of maximal voluntary isometric and isokinetic
strength characteristics of the knee extensor muscles in boys over puberty is consistent with earlier findings (1, 21, 23). This is mainly due to increase in muscle
size and body dimension as well as neural maturation. There is a rapid increase of
muscle strength in male children of approximately 13 years of age, corresponding
to increase in muscle mass (IS), cross-sectional area of muscles (17), and attainment of sexual maturity (4). The increase in secretion of testosterone at puberty
Knee Extensor and Vertical Jumping - 65
Figure 2 - Mean ( S E ) absolute and body mass-related values of isokinetic peak
(PT,) (A), 180"torque of the knee extensor muscles at angular velocities of 60" s1
s1
(PT,,) (B), and 240" s-I (PT,,) (C) in pre- and post-pubertal boys. **p < -01; ***p
< .MI.
66 - Paasuke, Ereline, and Gapeyeva
SJ
CMJ
DJ
Figure 3 -Mean ( S E )jumping height in squat jump (SJ), counter-movementjump
(CMJ), and drop jump (DJ) in pre- and post-pubertal boys. *p c -05; **p < .01.
has been associated with increase in skeletal muscle mass (20). It is possible that
neural maturation has contributed to the age effect for maximal isometric and
isokinetic force. It has been suggested that the expression of muscle strength is
dependent on myelination of the motor nerves, which is not completed until sexual
maturity (7). The maximal voluntary force-generation capacity of the muscles is
highly dependent upon the degree of motor unit activation (recruitment and change
of the firing rate of the muscle fibers), which is influenced by the development of
the central nervous system. Blimkie (4) has found that 16-year-old boys could
voluntarily activate a greater percentage of their available motor units during a
maximal voluntary contraction than 11-year-old boys.
The present study indicated a significantly higher (34%) rate of voluntary
isometric force development of the knee extensor muscles in post-pubertal boys
compared with pre-pubertal boys. The RFD in isometric and dynamic contractions
is related to the contractile speed. The maximum shortening speed determined
from the force-velocity curve is closely related to the shortening speed of sarcomeres, which correlates with myosin-ATPase activity (3). The activity of this enzyme in infants and pre-pubertal children is lower than in adults (10). The number
of sarcomeres increases, and as a necessary consequence, muscle length increases
with growth. Thus the contractile speed of the whole muscle in post-pubertal boys
seems to be faster compared to that in pre-pubertal boys. Moreover, contractile
speed is highly dependent upon motor unit activation: recruitment and change of
the firing rate of slow and fast twitch motor units in voluntary contraction. These
two mechanisms are influenced by factors as the development of the nervous system and the differentiation of muscle fiber types. Hence, the effects of the above
mentioned factors gradually increase with growth (12).
Knee Extensor and Vertical Jumping - 67
The changes in maximal voluntary muscle force per unit of body mass during
puberty is controversial. Several authors have observed a significantly higher
isokinetic PT of the knee extensor muscles in relation to body mass in post-pubertal
children compared with pre-pubertal children (9,26). However, others (13,25) have
reported age-related increase in isokineticPT of the knee extensor muscles that could
not be accounted for by changes in body mass. However, our data clearly indicated
that the increase in voluntary isokinetic strength over puberty was closely related to
increase in body mass, but maximal voluntary isometric force and rate of force development expressed per unit of body mass would appear to remain unchanged
through puberty. It is possible that these differences were attributable to differing
motor unit activation pattern between isometric and dynamic muscle contractions.
The vertical jumps can be used as a model to study explosive force-generating capacity of the lower extremities. In the present study, the vertical jumps were
performed without (SJ) and with preliminary counter-movement (CMJ and DJ).
CMJ and DJ are exercises characterized by so-called stretch-shortening cycle, in
which the action of the muscles during the eccentric phase influences the subsequent concentric phase (2,6). The results of the present study indicated that jumping height in SJ, CMJ, and DJ was 16%, 15%, and 16.8% lower in pre-pubertal
boys compared with post-pubertal boys, respectively. In general, this is in agreement with previous findings (1 1, 15). The differences between pre- and post-pubertal boys regarding their vertical jumping performance are conditioned by the
following factors. The vertical jumping height depends on the physiological processes that take place in the muscular and nervous systems. One finding of this
study was a significantly higher dynamic force generating capacity of the knee
extensor muscles in post-pubertal boys compared with pre-pubertal boys. It is well
known that dynamic force of the knee extensor muscles is one important factor
limiting performance in jumping exercises. Another important factor is intrarnuscular co-ordination and co-activation of activity of the agonist-antagonist muscles
involved in performing the jump (22). Thus, the greater vertical jumping performance in post-pubertal boys compared with pre-pubertal boys can be partly explained by an increase in the capacity for rapid neural activation of the extensor
muscles of lower extremities.
A significantlygreater height in jumping exercises with preliminary countermovement (CMJ or DJ) compared with SJ in adult subjects (2, 24) has been reported. Several mechanisms have been proposed to explain the positive effect of a
counter-movement on performance in the subsequent concentric action: (a) It allows for storage of elastic energy that can subsequently be re-utilized (2,6); (b) it
triggers spinal stretch reflexes as well as longer-latency responses (19) that help to
increase muscle stimulation during the concentric phase; and (c) it allows for greater
joint movements at the start of push-off and more work production (5). The results
of the present study indicated no significant differences between SJ, CMJ, and DJ
~-~~k~h~~~-;,"..-;n-pre-pubrtalarpostzpubertalalbopsSLand
therefore, that they cannot use the positive effect of a stretch-shortening cycle to
vertical jumping performance in counter-movement and drop jumps. However, the
question, how does stretch load (drop height) influence the vertical jumping performance in pre- and post-pubertal children, needs further detailed examination.
In summary, this study has shown that in boys the post-puberty compared
with pre-puberty is characterized by: (a) increased absolute values of maximal
voluntary isometric force and rate of force development as well as absolute and
68 - Paasuke, Ereline, and Gapeyeva
body mass-related values of isokinetic peak torque of the knee extensor muscles
and verticaljumping height, and (b) unchanged maximal voluntary isometric force
and rate of force development of the knee extensor muscles in relation to body
mass. The results demonstrated an inability to use the positive effect of the stretchshortening cycle to vertical jumping performance in counter-movement and drop
jumps in pre- and post-pubertal boys.
References
1. Alexander, J., and G.E. Molnar. Muscular strength in children: preliminary report on
objective standards. Arch. Phys. Med. Rehabil. 54:424-427, 1973.
2. Asmussen, E., and F. Bonde-Petersen. Storage of elastic energy in skeletal muscles in
man. Acta Physiol. Scand. 91:385-392, 1974.
3. Barany, M. ATPase activity of myosin correlated with speed of muscle shortening. J.
Gen. Physiol. 50:197-218, 1967.
4. Blimkie, C.J.R. Age- and sex-associated variation in strength during childhood: anthropometic, morphologic,neurologic, biomechanic, endocrinologic,genetic and physical activity correlates. In: Youth Exercise and Sport, C.V. Gisolfi and D.R. Lamb (Eds.).
Indianapolis, IN: Benchmark Press, 1989, pp. 99-163.
5. Bobbert, M.F., K.G. Gemtsen, M.C.A. Litjens, and A.J. van Soest. Why is countermovementjump height greater than squat jump height. Med. Sci. Sports Exerc. 28: 14021412,1996.
6. Bosco, C., A. Ito, P.V. Komi, I? Luhtanen, P. Rahkila, H. Rusko, and J. Viitasalo. Neuromuscular function and mechanical efficiency of human leg extensor muscles during
jumping exercises. Acta Physiol. Scand. 114:543-550, 1982.
7. Brooks, G.A., and T.D. Fahey. Exercise Physiology: Human Bioenergetics and ItsApplication. New York: Macmillan, 1985.
8. Davies, C.T.M., M.J. White, and K. Young. Muscle function in children. Eul: J. Appl.
Physiol. 52:lll-114, 1983.
9. De Ste Croix, M.B.A., N. Armstrong, and J.R. Welsman. Concentric isokinetic leg
strength in pre-teen, teenage and adult males and females. Biol. Sport 16:75-86, 1999.
10. Drachman, D.B., and D.M. Johnston. Development of a mammalian fast muscle: dynamic and biochemical properties correlated. J. Physiol. (Lond.) 234:29-42, 1973.
11. Ereline, J., J. Gapejeva, M. Palsuke, and A. Pehme. Neuromuscular performance characteristics in judoists at various age. In: Papers on Anthropology VI. Tartu: Tartu University Press, 1995, pp. 47-52.
12. Goldspink, G., and P.S. Ward. Changes in rodent muscle fibre types during post-natal
growth, undernutition and exercise. J. Physiol. (Lond.) 296:453-469, 1979.
13. Housh, T.J., G.O. Johnson, R.A. Hughes, D.J. Housh, R.J. Hughes, A.S. Fry, K.B.
Kennedy, and J. Cisar. Isokinetic strength and body composition of high school wrestlers across age. Med. Sci. Sports Exerc. 21:105-109, 1989.
14. Housh, T.J., G.O. Johnson, D.J. Housh, J.R. Stout, L.L. Weir, and J.M. Eckerson.
Isokinetic peak torque in young wrestlers. Ped. Exerc. Sci. 8: 143-155, 1996.
15. H i n e n , K., A. Mero, and H. Kauhanen. Specificity of endurance, sprint and strength
training on physical performance capacity in young athletes. J. Sports Med. Phys. Fim.
29~27-35,1989.
16. Ikai, M., and T.Fukunaga. Calculation of muscle strength per unit cross-sectional area
of human muscle by means of ultrasonic measurement. Int. Z. Angew. Physiol. 26:2632, 1968.
Knee Extensor and Vertical Jumping - 69
17. Kanehisa, H., S. Ikegawa, N. Tsunoda, and T. Fukunaga. Strength and cross-sectional
areas of reciprocal muscle groups in the upper arm and thigh during adolescence.Int. J.
Sports Med. 16:54-60, 1995.
18. Malina, R.M. Growth of muscle tissue and muscle mass. In: Human Growth. A Comprehensive Treatise: Postnatal Growth Neurobiology, Vol. 2, F. Faulkner and J.M. Tanner (Eds.). New York: Plenum Press, 1986, pp. 77-99.
19. Melvill Jones, G., and D.G.D. Watt. Observations on the control of stepping and hopping movements in man. J. Physiol. (Lond.)219:709-727, 1971.
20. Mero, A., L. Jaakkola, and P.V. Komi. Serum hormones and physical performance capacity in young boy athletes during 1-yeartraining period. Eur. J. Appl. Physiol. 60:3237, 1990.
21. Molnar, G.E., J. Alexander, and H. Gutfeld. Reliability of quantitative strength measurements in children. Arch. Phys. Med. Rehabil. 60:218-221, 1979.
22. Rack, P.M.H., and D.R. Westbury. The short range stiffness of active mammalian muscle
and its effect on mechanical properties. J. Physiol. (Lond.) 240:331-350, 1974.
23. Ramsay, J.A., C.J.R. Blirnkie, K. Smith, S. Garner, J.D. MacDougall, and D.G. Sale.
Strength training effects in prepubescent boys. Med. Sci. Sports Exerc. 22:605-614,
1990.
24. Riera, J., E Drobnic, P.A. Galilea, and V. Pons. Comparison of two methods for the
measurement of the extensor muscle dynamic force of the inferior limb: isokinetic
dynamometry and vertical jump tests. Sports Med. Training Rehabil. 5:37-43, 1994.
25. Seger, J.Y., and A. Thorstensson. Muscle strength and myoelectric activity in prepubertal and adult males and females. Eu,:J. Appl. Physiol. 69:81-87, 1994.
26. Sunnegardh, J., L.E. Bratteby, L.O. Nordesjo, and B. Nordgren. Isometric and isokinetic
muscle strength, anthropometry and physical activity in 8 and 13 year old Swedish
children. Eu,: J. Appl. Physiol. 58:291-297, 1988.
27. Tanner, J.M. Growth and Adolescence (2nd ed.). Oxford: Blackwell Scientific, 1962.