K. Klausen

Physiological Profile and Activity Pattern of Young Soccer Players during Match Play

PURPOSE The purpose of this study was to examine aerobic demands and activity patterns during match play in young soccer players with respect to competition level, age, and biological maturity. METHODS Ten nonelite players (NbP) and nine elite players (EbP) in their early puberty (12 yr), and seven elite players (EeP) in their late puberty (14 yr) were studied. Heart rate (HR) and activity pattern were recorded during match play, whereas corresponding .VO(2) and HR values were obtained during submaximal and maximal treadmill tests in the laboratory. The maturity status was assessed from testicular volume. RESULTS No difference in .VO(2max) was observed between the nonelite and the elite players in the beginning of puberty (58.7 +/- 5.3 vs 58.6 +/- 5.0 mL O(2).min-1.kg(-1)), whereas the elite players in the end of puberty were significantly more fit (63.7 +/- 8.5 mL O(2).min(-1).kg(-1)). During match play, a higher HR was recorded in the elite players in the beginning of puberty than their nonelite counterparts, whereas the two elite groups showed the same HR responses (HR 1st half/2nd half-NbP: 162/157; EbP: 177/174; EeP: 178/173). The elite players in the end of puberty thus performed a higher absolute and relative .VO(2) (.VO(2).min(-1) and mL O(2).min(-1).kg(-1)) compared with the nonelite players during both halves, corresponding to more time spent in standing/walking in the nonelite group. The elite players in the end of puberty showed higher absolute .V(O2) values during match play than the young elite players but identical relative aerobic loads. It seems that the midfield/attack group had the highest absolute .VO(2max) and was performing at the highest HR during the matches. CONCLUSION The present study shows that young soccer players are highly specialized both according to playing level and position on the field.

Mechanical and muscular factors influencing the performance in maximal vertical jumping after different prestretch loads.

The objective of the present work was to study the interaction between the tendon elasticity, the muscle activation-loading dynamics, specific actions of the biarticular muscles, preloading and jumping performance during maximal vertical jumping. Six male expert jumpers participated in the study. They performed maximal vertical jumps with five different preloads. The kinematics and dynamics of the jumping movements were analysed from force plate and high speed film recordings. The amount of elastic energy stored in the tendons of the leg extensor muscles was calculated by a generalised tendon model, and the muscle coordination was analysed by surface EMG. The best jumping performances were achieved in the jumps with low preloads (counter movement jumps and drop jumps from 0.3 m). A considerable amount of the energy imposed on the legs by prestretch loading was stored in the tendons (26 +/- 3%), but the increased performance could not be explained by a contribution of elastic energy to the positive work performed during the push off. During the preloading, the involved muscles were activated at the onset of the loading. Slow prestretches at the onset of muscle activation under relatively low average stretch loads, as observed during counter movement jumps and drop jumps from 0.3 m, prevented excessive stretching of the muscle fibres in relation to the tendon length changes. This consequently conserved the potential of the muscle fibres to produce positive work during the following muscle-tendon shortening in concert with the release of the tendon strain energy. A significant increase in the activity of m. rectus femoris between jumps with and without prestretch indicated a pronounced action of m. rectus femoris in a transport of mechanical energy produced by the proximal monoarticular m. gluteus maximus at the hip to the knee and thereby enhanced the transformation of rotational joint work to translational work on the mass centre of the body. The changes in muscle activity were reflected in the net muscle powers. Vertical jumping is like most movements constrained by the intended direction of the movement. The movements of the body segments during the prestretches induced a forward rotation and during the take off, a backward rotation of the body. A reciprocal shift in the activities of the biarticular m. rectus femoris and m. semitendinosus indicated that these rotations were counteracted by changes in the direction of the resultant ground reaction vector controlled by these muscles.(ABSTRACT TRUNCATED AT 400 WORDS)

Activity of mono- and biarticular leg muscles during sprint running

SummaryA cinematographic recording of the movements of the lower limbs together with simultaneous emg tracings from nine lower limb muscles were obtained from two male track sprinters during three phases of a 100 m sprint run. The extensor muscles of the hip joint were found to be the primary movers by acceleration of the bodys center of gravity (C.G.) during the ground phase of the running cycle. The extensors of the knee joint were also important in this, but to a minor extent, while the plantar flexors of the ankle joint showed the least contribution. The biarticular muscles functioned in a way different from the monoarticular muscles in the sense that they perform eccentric work during the flight and recovery phases and concentric work during the whole ground phase (support), whereas the monoarticular muscles are restricted first to eccentric work and then to concentric work during the ground phase. Furthermore, the biarticular muscles show variation (and rate of variation) in muscle length to a larger extent than the monoarticular muscles. Paradoxical muscle actions appear to take place around the knee joint, where the hamstring muscles, m. gastrocnemius, m. vastus laterialis and m. vastus medialis act as synergists by extending the knee joint during the last part of the ground phase.

Lumbar Curve, Trunk Muscles, and Line of Gravity with Different Heel Heights

The influence of different heel heights on the lumbar curve, pelvic inclination, trunk muscle activity, and the position of the line of gravity was examined in 18 healthy women. They were examined while standing on heel-supports, being 4.5 cm elevated, at the level of and 2.5 cm lower than the support of the forefoot, respectively (Figure 1). Each examination was preceeded by one-hour adaptation to a corresponding shoe type. With increasing heel height, the lumbar lordosis and the pelvis inclination were decreased. The back and abdominal muscles did not alter their activities. The position of the line of gravity kept the distance from the forefoot almost constant, but the ankle joint was shifted towards the line of gravity with increasing heel height.

Dynamics of the martial arts high front kick

Fast unloaded movements (i.e. striking, throwing and kicking) are typically performed in a proximo-distal sequence, where initially high proximal segments accelerate while distal segments lag behind, after which proximal segments decelerate while distal segments accelerate. The aims of this study were to examine whether proximal segment deceleration is performed actively by antagonist muscles or is a passive consequence of distal segment movement, and whether distal segment acceleration is enhanced by proximal segment deceleration. Seventeen skilled taekwon-do practitioners were filmed using a high-speed camera while performing a high front kick. During kicking, EMG recordings were obtained from five major lower extremity muscles. Based on the kinematic data, inverse dynamics computations were performed yielding muscle moments and motion-dependent moments. The results indicated that thigh deceleration was caused by motion-dependent moments arising from lower leg motion and not by active deceleration. This was supported by the EMG recordings. Lower leg acceleration was caused partly by a knee extensor muscle moment and partly by a motion-dependent moment arising from thigh angular velocity. Thus, lower leg acceleration was not enhanced by thigh deceleration. On the contrary, thigh deceleration, although not desirable, is unavoidable because of lower leg acceleration.

Oxygen uptake and heart rate responses to exercise performed with concentric and eccentric muscle contractions.

ABSTRACT.The aerobic energy cost and certain circulatory and ventilatory responses were studied in 2 human subjects performing work on a bicycle ergometer and employing either concentric (Wcon) or eccentric (Wccc) muscle contractions. Work was performed at intensities ranging from 15–130 Watt and at

Acute effects of cigarette smoking and inhalation of carbon monoxide during maximal exercise

SummaryThe acute effect of inhaling the smoke of three cigarettes was compared to the effect of inhalation of an amount of carbon monoxide (CO), giving the same CO-saturation of the arterial blood as smoking during rest and during maximal exercise on a Krogh cycle ergometer. Sixteen male subjects were tested in the morning (1) after about 8 h without smoking (control), (2) after inhalation of the smoke of three cigarettes (smoke), and (3) after CO-inhalation (CO). It was found that the average maximal rate of O2-uptake (

Effect of Pre-Existing High Blood Lactate Concentration on Maximal Exercise Performance

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