On the skilled plantar flexor motor action and unique electromyographic activity of ballet dancers

Plantar intrinsic foot muscle activity and its relationship with postural sway during tiptoe standing in ballet dancers and non-dancers

BACKGROUND

Minimizing postural sway during tiptoe standing is essential for ballet dancers. Investigation of the activity of the plantar intrinsic foot muscles (PIFMs) may provide insight into postural sway in dancers. Herein, we compared PIFM activity during tiptoe standing between dancers and non-dancers and examined its relationship with postural sway.

METHODS

We enrolled 14 female ballet dancers and 13 female non-dancers. Electromyography (EMG) amplitudes of 64 channels of PIFMs and center of pressure (COP) data were recorded during bipedal tiptoe standing tasks performed with ankle plantarflexion angles of 20°, 40°, and 60° (dancers only). The EMG amplitudes were normalized to those during the maximum voluntary contraction, and the muscle activity level and its coefficient of variation over time (EMG-CVtime) during the task were assessed. Standard deviations in the anteroposterior and mediolateral directions, velocity, and area were calculated from the COP data.

RESULTS

Most COP and EMG variables were significantly lower in dancers than in non-dancers in both the 20° and 40° tasks (p < 0.05). Significant correlations were found between most combinations of the COP and EMG variables in both the 20° and 40° tasks in the whole cohort (r = 0.468-0.807, p ≤ 0.014). In the 60° task in dancers, COP velocity was strongly correlated with EMG-CVtime (r = 0.700, p = 0.005).

CONCLUSION

These results provide novel evidence that the PIFMs do not require high activity, but rather that its low, steady activity is the key, to achieve less postural sway during bipedal tiptoe standing in dancers.

Sensing Technology for Assessing Motor Behavior in Ballet: A Systematic Review

Background

Human performance in classical ballet is a research field of growing interest in the past decades. Technology used to acquire data in human movement sciences has evolved, and is specifically being applied to evaluate ballet movements to better understand dancers’ profiles. We aimed to systematically review sensing technologies that were used to extract data from dancers, in order to improve knowledge regarding the performance of ballet movements through quantification.

Methods

PubMed, MEDLINE, EMBASE, and Web of Science databases were accessed through 2020. All studies that used motor control tools to evaluate classical ballet movements, and possible comparisons to other types of dance and sports movements were selected. Pertinent data were filled into a customized table, and risk of bias was carefully analyzed.

Results

Eighty studies were included. The majority were regarding classical ballet and with pre-professional dancers. Forty-four studies (55%) used two or more types of technology to collect data, showing that motion capture technique, force plates, electromyography, and inertial sensors are the most frequent ways to evaluate ballet movements.

Discussion

Research to evaluate ballet movements varies greatly considering study design and specific intervention characteristics. Combining two or more types of technology may increase data reliability and optimize the characterization of ballet movements. A lack of studies addressing muscle–brain interaction in dancers were observed, and given the potential of novel insights, further studies in this field are warranted. Finally, using quantitative tools opens the perspective of defining what is considered an elite dancer.

A comparison of the effects of different stretching methods on flexibility, muscle activity, and pain threshold in ballet dancers; a preliminary randomized controlled trial

BACKGROUND

The purpose of this study is to compare the effects of stretching methods on flexibility, muscle activation, and pressure pain threshold in ballet dancers, and to suggest an effective stretching method.

METHODS

Thirty-three ballet dancers were randomized to the static stretching group (n = 11), muscle energy technique stretching group (n = 11), and vibration-assisted stretching group (n = 11). The angle of hip joint extension in arabesque, activation of the rectus femoris in devéloppé, and pressure pain threshold on the rectus femoris in the sitting position were measured to compare the effects of the different stretching methods. Paired t-test was used to compare the pre and post-intervention findings within each group and one-way analysis of variance to compare the difference in the amount of changes among the groups.

RESULTS

The hip joint extension angles increased in all stretching methods (p < 0.05); however, vibration-assisted stretching and muscle energy technique stretching were more effective than static stretching (p < 0.05). The activation of the rectus femoris decreased in all groups (p < 0.05); however the muscle energy technique stretching group and vibration-assisted stretching group showed a significant decrease in muscle activation compared with the static stretching group (p < 0.05). The pressure pain threshold significantly improved only in the static stretching group (p < 0.05); and vibration-assisted stretching group (p < 0.05).

CONCLUSIONS

Compared with static stretching and muscle energy technique stretching, vibration-assisted stretching is a beneficial method for improving flexibility, muscle activation, and pressure pain threshold in ballet dancers.

Temporal and quantitative variability in muscle electrical activity decreases as dexterous hand motor skills are learned

Muscle activity changes quantitatively and temporally during the motor learning process. However, the association between variability in muscle electrical activity and the learning and performance of dexterous hand movements is not well understood. Therefore, we undertook this study to investigate the relationships between temporal and quantitative variabilities in muscle activity and the learning of motor skills. Thirty-eight healthy participants performed 30 trials of a task that measured the time taken to rotate two cork balls 20 times using their non-dominant hand. The electromyographic (EMG) activities of the abductor pollicis brevis (APB), first dorsal interosseous, and extensor digitorum (ED) muscles were recorded. Temporal and quantitative variabilities in the EMG activity were evaluated by calculating the coefficient of variation of the duration and area of EMG activation. As motor learning proceeded, the task was completed more quickly and the EMG variability decreased. For all three muscles, significant correlations were observed between individual participants’ ball rotation time and EMG variability. Furthermore, significant positive correlations were observed between improvement in ball rotation time and reduction in EMG variability for the APB and ED muscles. These novel findings provide important insights regarding the relationships between temporal and quantitative variabilities in muscle activity and the learning of fine motor skills.

Location of Reference Electrode Does Not Interfere on Electromyographic Parameters in the Domains of Time and Frequency

There is currently little information on the positioning of reference electrode (RE). It is generally accepted that it must be positioned on electrically neutral tissues, such as tendons or bony prominences. The objective of this study is to analyze the characteristics of the electromyographic signal (EMG) for different positions of RE as well as at different levels of muscle contraction. Signals from the brachial biceps and triceps were recorded from 18 healthy women (BMI: 21.20 kg/m² ± 1.72; mean age: 21.94 ± 1.98 years old) during 100 and 50% maximum flexion voluntary isometric contractions, as well as at rest. For each situation, the RE was randomly positioned in 4 different locations: a) homolateral acromion; b) homolateral brachial biceps; c) styloid process of the contralateral ulna; and d) lateral malleolus of the contralateral ankle. For statistical analysis, Shapiro-Wilk and Kruskal-Wallis tests were used, followed by Dunn's post-hoc test, at a significance level of 5% (p < 0.05). RMS, normalized RMS, PSD, median frequency and levels of energy at 60 Hz, 120 Hz and 180 Hz were assessed for the different sites of RE. The results show that the positioning of the RE on the four experimental locations did not change important features of the electromyographic signals in the time and frequency domains, for the three levels of isometric contractions studied. Such findings compel us to re-think the current trend regarding the RE position followed by the great majority of the researches in areas such as physical therapy.