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Intensity- and muscle-specific fascicle behavior during human drop jumps

¹Neuromuscular Research Center, Department of Biology of Physical Activity, University of Jyväskylä, Jyväskylä, Finland; and ²Laboratory of Biomechanics, Faculty of Sports, University of Porto, Porto, Portugal

Submitted 2 March 2006 ; accepted in final form 23 October 2006

	ABSTRACT

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The present study was designed to examine fascicle-tendon interaction in the synergistic medial gastrocnemius (MG) and soleus (Sol) muscles during drop jumps (DJ) performed from different drop heights (DH). Eight subjects performed unilateral DJ with maximal rebounds on a sledge apparatus from different DH. During the exercises, fascicle lengths (using ultrasonography) and electromyographic activities were recorded. The results showed that the fascicles of the MG and Sol muscles behaved differently during the contact phase, but the whole muscle-tendon unit and its tendinous tissue lengthened before shortening in both muscles. The Sol fascicles also lengthened before shortening during the ground contact in all conditions. During the braking phase, the Sol activation increased with increasing DH. However, the amplitude of Sol fascicle lengthening was not dependent on DH during the same phase. In the MG muscle, the fascicles primarily shortened during the braking phase in the lower DH condition. However, in the higher DH conditions, the MG fascicles either behaved isometrically or were lengthened during the braking phase. These results suggest that the fascicles of synergistic muscles (MG and Sol) can behave differently during DJ and that, with increasing DH, there may be specific length change patterns of the fascicles of MG but not of Sol.

stretch-shortening cycle; ultrasound; biarticular muscle; elasticity; inhibition

Repeated drop jumps (DJ) can be used to study fascicle behavior and are particularly suitable for investigating the utilization of tendinous tissue (TT) elasticity (10, 13). It has been suggested (13) that the fascicles of a biarticular muscle may not behave in the same way as those of a monoarticular muscle. However, this suggestion was based on a comparison between the MG and vastus lateralis (VL) muscles. During DJ, the relative muscle-tendon unit (MTU) lengthening of MG (5.2%) was less than that of VL muscle (11%).

In the triceps surae muscle group, only one study has shown that fascicles of the synergistic MG and Sol muscles behave differently during human walking (12). The MG fascicles were stretched during the early single-stance phase and then remained isometric during the late single-stance phase. In contrast, the Sol fascicles were lengthened throughout the single-stance phase. During this long contact phase of slow walking, the peak Achilles tendon load was quite low (<1,600 N). It is believed that this low-impact condition cannot be used to generalize the fascicle behavior of these muscles, as slow speed walking clearly differs from other forms of movement. Consequently, there is a need for a greater understanding of muscle-specific fascicle behavior during SSC movements that involve higher Achilles tendon loads.

The objectives of the present study were to investigate fascicle-TT interaction in a synergistic pair of muscles (MG and Sol) during DJ of different impact loading conditions. We hypothesized that, during the braking phase, the MG fascicles would shorten with low-impact loads. However, as the impact load increased [higher drop heights (DH) in DJ], the MG fascicles would shorten less during the braking phase and actually lengthen when the impact load was extremely high. In the Sol muscle, on the other hand, the fascicles were always expected to lengthen, regardless of the stretch (impact) condition. Both of these hypotheses suggest that, during high-impact SSC movements, the MG muscle is much more sensitive than the Sol muscle to variations of the impact load. It must be emphasized that, to the best of our knowledge, with the exception of human walking (12), the Sol fascicle-TT interaction has not previously been studied under natural stretch (impact) conditions, while simultaneously studying the MG muscle.

	METHODS

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Subjects and experimental procedure.   Eight physically active subjects, age 26.6 yr (SD 2.8), height 170.1 cm (SD 6.8), and body mass 61.9 kg (SD 9.9), participated in this study. Before testing, subjects were familiarized with the sledge DJ exercises and provided written, informed consent. The study was approved by the Ethics Committee of the University of Jyväskylä.

The lowest position of the sledge seat was determined at rest with knee and ankle angles of 50 and 85°, respectively (0° is full extension). The subjects then performed several unilateral (right leg) maximum DJ from different DHs on the sledge apparatus (9–11, 21) to decide the optimal DH for each subject. This was determined by dropping the subject from different heights to find the greatest rebound height of the center of gravity (13, 19). Thereafter, subjects performed the DJ with maximal rebounds from four individually predetermined DHs: 50, 75, 100, and 120% of the optimal DH (DJ1, DJ2, DJ3, and DJ4, respectively), in a random order. Unilateral jumps were chosen to ensure a higher relative impact load compared with bilateral jumps. To obtain the same condition bilaterally would not have been possible using our sledge apparatus. In the present study, the sledge inclination was set to 43° above the horizontal position. During the jumping tasks, the lowest sledge seat position (see above) and maximal jump height were confirmed by monitoring signals of the position sensor attached to the sledge seat during trials. Three successful trials were required for each task.

Reaction forces [vertical force (F_z); parallel to the movement plane of the sledge seat], sledge displacement, velocity of sledge displacement, and EMG activity of the MG and Sol muscles of the right leg were stored simultaneously on a personal computer via an analog-to-digital converter (sampling rate 2 kHz; Power 1401, Cambridge Electronics Design). Surface bipolar EMG electrodes were used to record the MG and Sol muscle activities (Ag-AgCl miniature surface bipolar electrodes, interelectrode distance of 20 mm; Beckman skin electrode 650437). To place the EMG electrodes on the muscle belly, B-mode ultrasound images were used to precisely locate the MG muscle midbellies for each subject.

EMG signals were amplified (input impedance 25 M, common mode rejection ratio >90 dB) and then sent telemetrically to the analog-to-digital converter. The skin was lightly treated with sandpaper to secure an interelectrode resistance value <5 k.

All DJs were recorded with a high-speed video camera (200 frames/s; Peak Performance) from the subjects’ right side, perpendicular to the plane of motion, to calculate the joint angles of the lower limb (knee and ankle). Reflective markers were placed over the center of rotation of the shoulder, trochanter major, center of rotation of the knee, lateral malleolus, heel, and fifth metatarsal head. The markers were then digitized automatically using Peak Motus software (Peak Performance). The transformed coordinates were digitally filtered with a Butterworth fourth-order, zero-lag, low-pass filter (cut-off frequency: 8 Hz). Longitudinal images of the MG and Sol muscles of the right leg were obtained during movement using a real-time B-mode ultrasound apparatus (SSD-5500, Aloka). An adhesive silicon pad was placed between the skin and the ultrasound probe to avoid any movement of the probe relative to the muscle belly. The probe was fixed securely with a special support device made of polystyrene. The ultrasound apparatus was used to measure two-dimensional fascicle lengths (L_fa) in the MG and Sol muscles during the DJ (96 images/s, 6-cm linear array probes with scanning frequency 10 MHz; Aloka) (7, 12, 13). The width and depth (thickness) of the scanning images were 5.91 cm (330 pixels) and 5.38 cm (248 pixels), respectively. The superior and inferior aponeuroses, and the MG and Sol fascicles, were identified and digitized in each image (7, 12, 13, 16) (Fig. 1). The reliability of the ultrasound method of L_fa calculation has been established elsewhere, with a coefficient of variation ranging between 0 and 6% (6, 14, 15, 16, 20). An electronic pulse was used to synchronize the EMG, kinetic, kinematic, and ultrasonographic data.

View larger version (70K): [in this window] [in a new window]   Fig. 1. A typical example of a sequence of longitudinal ultrasonic images of medial gastrocnemius (MG) and soleus (Sol) during drop jumps (DJ). Each longitudinal ultrasonic image was recorded at 96 Hz.

where L_TT is the TT length, and is the angle between the fascicle line and the aponeurosis (pennation angle). The TT strain was estimated from the length change of TT from the moment of contact to the moment of peak L_TT, divided by the L_TT at the moment of contact.

EMG signals were full-wave rectified and low-pass filtered at 75 Hz (Butterworth type fourth-order low-pass digital filter). The filtered EMG signals were integrated and then averaged (aEMG) individually and separately for the following three phases during the ground contact of DJ: preactivation, braking, and push-off. The preactivation phase was defined as the 100-ms period preceding ground contact. The transition from the braking phase to the push-off phase was determined while the sledge was at its lowest position.

Statistics.   Values are presented as means and SDs, unless otherwise stated. To analyze the differences between the different DH conditions for the sledge speed and F_z, a repeated-measures one-way ANOVA was used, with a post hoc least significant difference multiple comparison. A multivariable ANOVA was used to assess the differences in the EMG and length data, as well as interactions of the DH intensity with each muscle, and of the DH intensity with each phase. If interactions were present, a post hoc Tukey was used to test the difference between them. Spearman’s rank correlation coefficient for polynomial regression analysis of variables was used to calculate the statistical significance of the relationship between the dropping sledge speed and the fascicle stretch amplitude. The probability level accepted for statistical significance was P < 0.05.

	RESULTS

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Changes in mechanical parameters.   As shown in Table 1, the sledge jump performances were in accordance with our hypotheses: the peak F_z and the peak dropping speed increased significantly from DJ1 to DJ4, and the corresponding peak rebound speeds increased until DJ3 (optimal DH). DJ4 was intended to represent an excessive DH (prestretch speed), and the resulting peak rebound speed of 1.13 ± 0.09 m/s showed no significant increase compared with DJ3 (1.20 ± 0.11 m/s). Although there was no significant change in total contact time, the duration of the braking phase decreased in DJ3 and DJ4 compared with DJ1 (Table 1).

View larger version (7K): [in this window] [in a new window]   Fig. 2. Averaged electromyogram (EMG) values (±SD) for MG and Sol muscles in the preactivation, braking, and push-off phases for all dropping conditions [DJ at 50, 75, 100, and 120% of optimal drop height (DH) (DJ1, DJ2, DJ3 and DJ4, respectively)]. Significantly different from DJ1 at *P < 0.05 and **P < 0.01. Significantly different from DJ2 at #P < 0.05 and ##P < 0.01.

View larger version (48K): [in this window] [in a new window]   Fig. 3. Representative example of the time course data of the lengths of the MG and Sol muscle-tendon units (MTU), tendinous tissue (TT), and fascicle, together with the EMG activity of the MG and Sol muscles. The 0.0 in the x-axis shows the contact moment of the DJ. The "% of standing" in the y-axis for the first 3 rows shows the relative changes from the length in the upright position. Vertical dotted lines show the points of the contact, end of the braking phase, and take-off.

View larger version (18K): [in this window] [in a new window]   Fig. 4. Amplitudes of stretch (top) and shortening (bottom) in the braking and push-off phases for MTU and TT of the MG and Sol muscles, for all dropping conditions (DJ1, DJ2, DJ3, and DJ4). Significantly different between conditions at *P < 0.05 and **P < 0.01. Significantly different between MTU and TT at #P < 0.05 and ##P < 0.01.

View larger version (11K): [in this window] [in a new window]   Fig. 5. Calculated peak TT strains of the MG and Sol during DJs under the different DH conditions. The bars show group means + SD. The strain was calculated from the length at the initial contact to the length at the peak TT stretch during contact divided by the TT length at the initial contact. There was a significant increase in the TT strain of Sol when the DH increased (*P < 0.05).

	DISCUSSION

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To enable examination of the influence of DH on L_fa changes during the braking phase, Fig. 6 plots these attributes against each other for this particular phase. The length change patterns tend to have an opposite quadratic relationship with the prestretch intensity (dropping speed). In the MG muscle, there may be a critical level of the stretch load (DH), beyond which the MG fascicles lose their ability to tolerate the imposed load (Fig. 6A). It is interesting to note that the result shown in Fig. 6A is almost identical to that presented in a previous report (13), despite the fact that the SSC exercise differed between these studies. These results further emphasize the difference in fascicle behavior of MG and Sol during DJ and again suggest that there may be specific length-change patterns of the MG and Sol fascicles, depending on the DH.

View larger version (22K): [in this window] [in a new window]   Fig. 6. The slope of MG (A) and Sol (B) fascicle length changes (Lfa) vs. the peak dropping speed of the sledge displacements in the braking phase (n = 8). The solid circles and bars show the averaged data and SEs. Inset: how the Lfa were calculated during the braking phase (see also Ref. 13). NS, not significant.

View larger version (12K): [in this window] [in a new window]   Fig. 7. Relationship between the stretches of the fascicles and MTU during the DH conditions for the MG and Sol muscles (circles: MG, triangles: Sol). A: absolute stretch lengths from the contact to the end of the braking phase. B: the same phenomena in a relative scale calculated from the moment of contact.

When a similar exercise protocol using different contact times (bilateral DJ) was used to observe MG fascicle behavior (13), the results were identical to those of the present study. However, the Sol muscle was not investigated in the previous study (13). In the present study, the behavior of Sol differed from MG in several ways. In the preactivation and braking phases, muscle activity tended to be higher in DJ4 than DJ3 in Sol, but not in MG (Fig. 2). At the end of the braking phase, the corresponding Sol L_fa was shorter in DJ4 than in DJ3 (the only significant difference was between DJ2 and DJ4, Table 2). This suggests that the Sol muscle is still able to function "normally" without any additional rapid L_fa changes (MG).

It would be beneficial to discuss the results from the perspective of neural influences. The results presented in Fig. 3 and Table 2 may help to clarify the findings obtained in studies in which running and various intensity hopping exercises were used. Voigt et al. (27) reported that, in the Sol muscle, the SLR in SSC is very apparent and easier to record than in the MG muscle during submaximal hopping. In contrast, Dietz et al. (2) observed the SLR responses in MG during running, and Moritani et al. (22) reported that the amplitude of H-reflex modulation was higher in MG than in Sol during maximal effort hopping. In the present study, the fascicles of MG shortened during the braking phase of the DJ1 and DJ2 conditions, whereas those of Sol were stretched (Fig. 3). However, with higher impact loads (DH), the MG fascicles were stretched during the late-braking phase (in DJ4) (Fig. 3), whereas the Sol fascicles exhibited similar behavior (stretching-shortening) in all DH conditions (Table 2). These results can partially explain the different results of Voigt et al. (27), Dietz et al. (2), and Moritani et al. (22, 23). One may conclude that, during the braking phase of DJs, DH- and muscle-specific L_fa changes may influence the stretch-induced muscle activation.

It has been suggested that, in extremely high DJ exercises, inhibitory effects from the Golgi tendon organ may be operative. It would, therefore, be useful to know if there are any differences in inhibitory inputs to the two muscles in DJs. In the present results, the MG aEMG did not increase from DJ3 to DJ4 (Fig. 2) during the braking phase, but the MG fascicles were stretched during the braking phase in DJ4 (Figs. 3, 6, and 7). During the same phase in the Sol muscle, however, the aEMG increased, and the stretch amplitude of the Sol fascicles showed no difference between DJ3 and DJ4, or was actually lower in DJ4 (Figs. 6 and 7, Table 2). One may speculate that, while the MG muscle receives less facilitatory Ia afferent input [the muscle spindle content is greater in Sol than MG (17)], the same amount of Ib input would have greater inhibitory influences on the MG than on the Sol muscle. Therefore, the difference in muscle spindle content between the respective muscles may partially account for the observed differences in fascicle behavior in response to changes in DH. This assumption may also be influenced by additional unknown factors, such as the possibility that the induced stretch loads have equal excitatory effects on the activation of Ib afferents in both muscles. However, it is still difficult to explain how the possible inhibitory influences, for example, from the Golgi tendon organs, would operate differently between the two synergistic muscles.

In the previous study (13), our major argument was that the "yielding" that occurred in conjunction with fascicle lengthening was due to sudden cross-bridge detachment in high DH conditions. The present results show that the MG fascicles were stretched during the braking phase of DJ4 (Fig. 3). The contact times of the braking phase were twice as long in the present study (200 ms) compared with the previous one (13) (<100 ms). Therefore, the sudden cross-bridge detachment may not have occurred to the same extent as in the DJ condition of the previous study (13). This can be seen from the slopes of the fascicle stretch, which were approximately twice as steep in the previous study (13). It has been suggested that the reduction in DJ performance during the extremely high DH condition can be affected by neural inhibition, as well as by mechanical cross-bridge slipping (or detachment) (c.f., Ref. 13). In the present study, inhibitory effects from the Golgi tendon organ, if present, may have been mainly operative in the performance reduction that was observed in the long-contact, extremely high-DJ condition (DJ4).

Whatever the possible mechanism, the observed intermuscular differences in fascicle behavior are very important findings of the present study. The results suggest that the whole concept of the SSC of muscle function should be critically assessed, especially regarding the way in which fascicles interact with TT during normal locomotion. An equally important consideration is that the fascicle behavior is task dependent, at least in some muscles. For example, there is a preferential and movement-phase-dependent neuromuscular activation within the synergistic human ankle extensor muscles (23). In addition, and as shown in the present study, the preactivation may be DH dependent (see also Refs. 11, 13). There are, however, reports in the literature that question the interdependence of DH and EMG preactivation (1). Dietz (3), while supporting the idea of intensity-dependent preactivation, suggested that foot positioning and anticipation of the moment of ground contact may be critical factors for preactivation.

In summary, the results of the present study highlight differences in fascicle behavior of synergistic muscles (MG and Sol) during DJ exercises. Moreover, the fascicle behavior in response to changes in DH differed between the two muscles, whereas the EMG activities of these muscles showed a clear relationship with DH. Although some of these observations had been made previously to a certain degree (11, 13), the present comparison with simultaneous recording of two synergistic muscles serves to further emphasize the above-mentioned differences (4, 9, 21, 25).

	GRANTS

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The study was supported by Grant 88/627/2005 (P. V. Komi) from the Ministry of Education, Finland.

	ACKNOWLEDGMENTS

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The authors gratefully acknowledge P. Puttonen for assistance during the measurement and N. Cronin for checking the English language.

	FOOTNOTES

 

Address for reprint requests and other correspondence: M. Ishikawa, Neuromuscular Research Center, Dept. of Biology of Physical Activity, Univ. of Jyväskylä, 40014 Jyväskylä, Finland

The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

	REFERENCES

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1. Arampatzis A, Schade F, Walsh M, Bruggemann GP. Influence of leg stiffness and its effect on myodynamic jumping performance. J Electromyogr Kinesiol 11: 355–364, 2001.[CrossRef][ISI][Medline]
2. Dietz V, Schmidtbleicher D, Noth J. Neuronal mechanisms of human locomotion. J Neurophysiol 42: 1212–1222, 1979.[Abstract/Free Full Text]
3. Dietz V. Human neuronal control of automatic functional movements: interaction between central programs and afferent input. Physiol Rev 72: 33–69, 1992.[Free Full Text]
4. Elftman H. The function of muscles in locomotion. Am J Physiol 125: 339–356, 1939.[Free Full Text]
5. Fukashiro S, Itoh M, Ichinose Y, Kawakami Y, Fukunaga T. Ultrasonography gives directly but noninvasively elastic characteristic of human tendon in vivo. Eur J Appl Physiol Occup Physiol 71: 555–557, 1995.[CrossRef][ISI][Medline]
6. Fukunaga T, Ichinose Y, Ito M, Kawakami Y, Fukashiro S. Determination of fascicle length and pennation in a contracting human muscle in vivo. J Appl Physiol 82: 354–358, 1997.[Abstract/Free Full Text]
7. Fukunaga T, Kubo K, Kawakami Y, Fukashiro S, Kanehisa H, Maganaris CN. In vivo behaviour of human muscle tendon during walking. Proc R Soc Lond B Biol Sci 268: 229–233, 2001.[Medline]
8. Hawkins D, Hull ML. A method for determining lower extremity muscle-tendon lengths during flexion/extension movements. J Biomech 23: 487–494, 1990.[CrossRef][ISI][Medline]
9. Horita T, Komi V, Hamalainen I, Avela J. Exhausting stretch-shortening cycle (SSC) exercise causes greater impairment in SSC performance than in pure concentric performance. Eur J Appl Physiol 88: 527–534, 2003.[ISI][Medline]
10. Ishikawa M, Finni T, Komi PV. Behaviour of vastus lateralis muscle-tendon during high intensity SSC exercises in vivo. Acta Physiol Scand 178: 205–213, 2003.[CrossRef][ISI][Medline]
11. Ishikawa M, Komi PV. Effects of different dropping intensities on fascicle and tendinous tissue behavior during stretch-shortening cycle exercise. J Appl Physiol 96: 848–852, 2004.[Abstract/Free Full Text]
12. Ishikawa M, Komi PV, Grey MJ, Lepola V, Bruggemann GP. Muscle-tendon interaction and elastic energy usage in human walking. J Appl Physiol 99: 603–608, 2005.[Abstract/Free Full Text]
13. Ishikawa M, Niemela E, Komi PV. Interaction between fascicle and tendinous tissues in short-contact stretch-shortening cycle exercise with varying eccentric intensities. J Appl Physiol 99: 217–223, 2005.[Abstract/Free Full Text]
14. Ishikawa M, Pakaslahti J, Komi PV.Medial gastrocnemius muscle behavior during human running and walking. Gait Posture. In press.
15. Kawakami Y, Ichinose Y, Fukunaga T. Architectural and functional features of human triceps surae muscles during contraction. J Appl Physiol 85: 398–404, 1998.[Abstract/Free Full Text]
16. Kawakami Y, Muraoka T, Ito S, Kanehisa H, Fukunaga T. In vivo muscle fibre behaviour during counter-movement exercise in humans reveals a significant role for tendon elasticity. J Physiol 540: 635–646, 2002.[Abstract/Free Full Text]
17. Kokkorogiannis T. Somatic and intramuscular distribution of muscle spindles and their relation to muscular angiotypes. J Theor Biol 229: 263–280, 2004.[CrossRef][ISI][Medline]
18. Komi PV. Stretch-shortening cycle: a powerful model to study normal and fatigued muscle. J Biomech 33: 1197–1206, 2000.[CrossRef][ISI][Medline]
19. Komi PV, Bosco C. Utilization of stored elastic energy in leg extensor muscles by men and women. Med Sci Sports Exerc 10: 261–265, 1978.
20. Kurokawa S, Fukunaga T, Fukashiro S. Behavior of fascicles and tendinous structures of human gastrocnemius during vertical jumping. J Appl Physiol 90: 1349–1358, 2001.[Abstract/Free Full Text]
21. Kyrolainen H, Komi PV. Differences in mechanical efficiency between power- and endurance-trained athletes while jumping. Eur J Appl Physiol Occup Physiol 70: 36–44, 1995.[CrossRef][ISI][Medline]
22. Moritani T, Oddsson L, Thorstensson A. Differences in modulation of the gastrocnemius and soleus H-reflexes during hopping in man. Acta Physiol Scand 138: 575–576, 1990.[ISI][Medline]
23. Moritani T, Oddsson L, Thorstensson A. Phase-dependent preferential activation of the soleus and gastrocnemius muscle during hopping in humans. J Electromyogr Kinesiol 1: 33–40, 1991.[Medline]
24. van Ingen Schenau GJ, Bobbert MF, Rozendal RH. The unique action of bi-articular muscles in complex movements. J Anat 155: 1–5, 1987.[ISI][Medline]
25. van Ingen Schenau GJ, Bobbert MF, van Soest AJ. The unique action of bi-articular muscles in leg extensions In: Multiple Muscle System, edited by Winters JM and Woo SL. New York: Springer, 1990, p. 639–352.
26. van Ingen Schenau GJ, de Koning JJ, de Groot G. Optimisation of sprinting performance in running, cycling and speed skating. Sports Med 17: 259–275, 1994.[ISI][Medline]
27. Voigt M, Dyhre-Poulsen P, Simonsen EB. Modulation of short latency stretch reflexes during human hopping. Acta Physiol Scand 163: 181–194, 1998.[CrossRef][ISI][Medline]

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This Article Abstract Full Text (PDF) Free All Versions of this Article: 102/1/382    most recent 00274.2006v1 Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (2) Citing Articles via Google Scholar Google Scholar Articles by Sousa, F. Articles by Komi, P. V. Search for Related Content PubMed PubMed Citation Articles by Sousa, F. Articles by Komi, P. V.