Bilateral Deficit in Vertical Jumping in Pre-Pubertal Boys and Girls

IntroductionThe bilateral deficit in vertical jumping occurs when the summed unilateral jump height is greater than the bilateral jump height. This phenomenon has been described in early studies involving maximal voluntary isometric contractions of the legs in adult populations (Secher et al., 1978) and has been attributed to a reduced neural drive and failure to activate maximally the muscles of the two limbs when they contract together (Vandervoort et al., 1984; Kawakami et al., 1998). The bilateral deficit has been observed in both trained and untrained individuals (Secher et al., 1988; Archondides & Fazey, 1993) while the magnitude of the reduction in maximal isometric force may range from -3 to -25% (Secher et al., 1978, 1988)The bilateral deficit has also been observed in explosive movements such as dynamic leg press (Hay et al., 2006) and vertical jumping (van Soest et al., 1985; Challis, 1998; Bobbert et al., 2006), but the proposed mechanisms explaining it at these movement patterns are not confined to neural drive, but are extended to muscle mechanics (Bobbert et al., 2006) and changes in muscle coordination patterns (Rejc et al., 2010). However, the reduction in two-legged jumps compared with the sum of one leg jumps is similar to that seen in isometric force (-17% to -20%; van Soest et al., 1985; Challis, 1998). There are very limited data on bilateral deficit in young individuals. Kuruganti & Seaman (2006) examined the bilateral leg strength deficit in old, young and adolescent females using isokinetic knee exercise. They examined an adolescent population and found a bilateral deficit ranging from -20 to -32% that was similar in all age groups, with no change in myoelectric signal. It was suggested that the deficit was not solely the result of reduced motor unit activation. There is only one study comparing bilateral deficit between pre-pubertal, pubertal and post-pubertal males and females (Dunstheimer et al., 2001). However, testing was performed with one or two legs on a cycle ergometer, where participants sprinted for 30 s. The bilateral deficit in peak and mean power ranged from -8 to -20% and was more pronounced in females.To our knowledge, no data exist on bilateral deficit in vertical jumping in pre-pubertal children. Since vertical jumping from one leg is a task that demands balance, coordination and power, the bilateral deficit may be different from that observed in static or seated exercise (e.g. Dunstheimer et al., 2001). Moreover, the decreased ability of pre-pubertal children to activate motor units may further affect bilateral deficit and this may change with maturation (Paasuke et al., 2000). Therefore, the purpose of the present study was to compare bilateral deficit in jumping between pre-pubertal boys and girls, taking into account biological maturation.Material & methodsParticipantsOne hundred and seventy two pre-pubertal children (83 boys and 89 girls) took part in this study. Participants were divided according to gender and their chronological age into two groups (10 and 12 years). The physical characteristics of the participants are shown in Table 1.All children had experience in vertical jumping with one and two legs and were thoroughly familiarized with the measurements in three preliminary sessions. Prior to data collection, informed consent was obtained from a parent of each participant, after thorough description of the measurements to both the athletes and their parents. Training history was obtained by a personal interview. The study was approved by the local Institutional Review Board and all procedures were in accordance with the World Medical Association's declaration of Helsinki, as revised in 2008.Data collection and analysisAnthropometry: All measurements were taken in the morning (between 9:00 and 11:00) following standardized protocols (Lohman et al., 1988). Body mass was measured to the nearest 0. …