Journal of Dance Medicine & Science

One hallmark of dance education is rigor-ous and repetitive physical practice. Of the many unifying theories of motor learning, the “power law of practice” states that repetitive practice of physical movements is a necessary ingredient in improving performance. Compelling evidence exists, however, showing that practice conditions where rest intervals are interspersed be-tween movement repetitions (“distributed practice”) play a strategic role in the acqui-sition and consolidation of learning motor skills. Further, repetition without adequate rest is implicated in overuse syndrome and has injurious consequences in both the peripheral and central nervous system. This article summarizes the research from neuroscience and motor learning on distributed practice conditions within the context of overuse injuries in dance. The neural consequences of repetitive movement without rest (adequate rest-to-activity ratios) are discussed. Schedules designed to promote motor skill learning and avoid overuse (adopted in somatic education, sports, and martial arts) are reviewed in the light of the current philosophy underlying dance practice schedules. Finally, the paper points to need for future research in designing protocols with higher rest-to-activity ratios in dance classes.

While electromyographic (EMG) and ki-nematic data in dance are accumulating, to date these data have raised more questions than they have answered. The purpose of this study was to introduce ensemble averaging into this body of literature as a way of dealing with the high levels of within-subject and between-subject vari-ability that have been previously reported. This study also introduces analysis during a forward weight shift, an analysis currently absent from the literature. Three collegiate novices (18.7 ± 0.6 years of age) and three expert dancers (27.7 ± 5.5 years of age) were studied in-depth. EMG data were collected continuously at 600 Hz for analysis of onset of activity for abdominal and erector spinae muscles. Kinematic data were collected continuously at 120 Hz from markers on the acromion and the greater trochanter for analysis of the verticality of the trunk. Data were collected continuously for over 4 seconds to include: baseline data prior to movement on a right legged balance, data for movement into plié fondu on the right leg, data for a forward step to the left leg, and baseline data at resolution on a left legged balance. For analysis, data were synchronized by time using onset of vertical ground reaction forces recorded by a force plate under the initial stance leg. All participants were tested on two separate days to assess day-to-day variability. Fifteen trials were collected on each day for each individual. Ensemble averaging of continuously recorded data was used to create line graphs for visual inspection, first to compare day-to-day congruence for each individual, next to assess within group variability, and finally to compare composite graphs between groups. Day-to-day variations for each individual were minimal. Differences were seen between members of the Beginner group but not the Expert group. Between group comparisons revealed the following differences: Experts appeared to use an anterior core support strategy while Beginners appeared to use a posterior core support strategy, Experts dis-played less EMG and kinematic variability than Beginners, and Experts maintained a more vertical posture throughout. Surprisingly, even though Experts were more verti-cal, they demonstrated the same amount of overall anterior-posterior sway as the Beginners. This finding leads to discussion of the dynamic nature of neuromuscular coordination patterns in maintenance of verticality. Issues surrounding the inability of statistically constructed models of human kinematic data to accurately represent individuals in groups are also discussed. Finally, applications of these findings to teaching and learning are offered.

This article reviews the neuroscience of the Golgi tendon organ, a type of muscle sensory receptor. The intent is also to update and correct erroneous notions regarding its functional significance, particularly related to its involvement in reflexes, proprioception, and stretching techniques used in dance training. Historical research about the function of the Golgi tendon organ (GTO) has led to four erroneous views: 1. The GTO serves a protective function by responding only to muscle tension at the extreme end-range of motion; 2. Sensations from GTOs do not reach the cerebral cortex and therefore serve no role in conscious proprioception and kines-thesia; 3. The GTO and its reflex circuit (autogenic inhibition) prevent its muscle from contracting by “turning it off”; and 4. During contract-relax stretching, the GTO autogenic inhibition reflex circuit is responsible for the muscle relaxation phase and the accompanying increased range of motion.

Recent research has shown that these early views are inaccurate. There is new evidence regarding the role of the GTO. 1. A GTO responds to even weak active contractions throughout the range of motion, although GTOs are much less sensitive to passive tension than to active tension. 2. GTO sensations probably do reach the cerebral cortex, buried in the fissure between the motor and sensory cortex “strips.” This information allows dancers to know where their limbs are in space. GTOs also provide unconscious proprioception, via the cerebellum, which helps dancers to learn new motor skills and improve execution of movements. 3. The GTO and its reflex (autogenic inhibition) reduce, but do not shut off, the excitability of the motor neuron and its innervated muscle. The ultimate reflex effect depends on the sum of multiple other inputs on the motor neuron. GTO input may reduce muscle activity, but does not “turn it off.” 4. During contract-relax stretching, the GTO autogenic reflex creates inhibition that lasts only as long as the muscle's active contraction. Therefore, GTO activity is unlikely to significantly affect the subsequent relaxation phase of the stretch. Other receptors and spinal circuits likely serve this function. It is hoped that this updated information will correct several erroneous notions about GTOs that have persisted in the dance kinesiology literature. Thus, dance kinesiology teachers, researchers, and health practitioners can provide accurate information to their students, readers, and patients.

The purpose of this study was to investigate hip net joint moments in the gesture and support legs in grand rond de jambe en l'air en dehors. Two groups of dancers, skilled (N = 8) and novice (N = 6), performed grand rond de jambe en l'air at two different vertical leg angles: 90° and 105°. Three-dimensional motion data and ground reaction force data were collected. Hip net joint moments were computed through standard inverse dynamics procedures and were normalized to each participant's mass. Normalized peak hip joint moments in both the gesture and support leg were used as the dependent variables; the independent variables were the skill level and the demand (vertical angle for the rond de jambe at 90° and 105°). A two-way mixed-design ANOVA (2 groups x 2 conditions) was used (p < .05) with the group and demand as the between and within factors, respectively. The hip joint moments of the support leg were consistently larger than the matching moments of the gesture leg. However, as the demand level increased the peak hip joint moments of the gesture leg hip showed minor changes, the support leg moments decreased. It was concluded that muscular strength is not a limiting factor for the novice dancers and that an increased demand (vertical leg angle) actually puts smaller burden on the support leg hip. Increased pelvis movement (demonstrated by the skilled dancers) facilitated the range of motion of the gesture leg without increasing joint moment cost. The hip abductor moments were identified as im-portant components in performing grand rond de jambe en l'air.