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Updated: Jun 21, 2026
Chicken Recombinant Limbs Assay to Understand Morphogenesis, Patterning, and Early Steps in Cell Differentiation
Published on: January 12, 2022
Precocious locomotor behavior begins in the egg: development of leg muscle patterns for stepping in the chick
1Division of Biokinesiology and Physical Therapy, University of Southern California, Los Angeles, CA, USA.
Insights
Embryonic chick leg movements at embryonic day 18 (E18) show patterns similar to hatching locomotion. These precocious, repetitive movements are crucial for developing adaptive locomotor skills after hatching.
Area of Science:
- Developmental Biology
- Neuroscience
- Biomechanics
Background:
- Chicks exhibit advanced locomotor skills shortly after hatching.
- Embryonic leg movements during the final incubation week were previously understudied.
- Investigating these movements reveals insights into the development of motor control.
Purpose of the Study:
- To analyze leg muscle activity patterns in late-stage chick embryos.
- To determine if embryonic leg movements resemble post-hatching locomotion.
- To assess the influence of the eggshell environment on embryonic movement patterns.
Main Methods:
- Electromyograms, force, and video of leg muscles were recorded from embryos at embryonic days 15, 18, and 20.
- Shell removal was used to test the effects of posture and constraint.
- Bilateral coordination of ankle muscles was examined at embryonic day 20.
Main Results:
- By embryonic day 18, muscle activation patterns showed similarities to hatching locomotion.
- Muscle burst durations did not correlate with step cycle duration.
- Leg movement and muscle activity were largely unaffected by shell removal, with some exceptions.
- Ankle muscles demonstrated a left/right alternating pattern, indicating coordinated movement.
Conclusions:
- Embryonic leg movements are linked to the development of locomotor abilities.
- These findings highlight a critical developmental stage for motor skill acquisition.
- The study provides a foundation for understanding the neural and muscular basis of early locomotion.
Background:
The chicken is capable of adaptive locomotor behavior within hours after hatching, yet little is known of the processes leading to this precocious skill. During the final week of incubation, chick embryos produce distinct repetitive limb movements that until recently had not been investigated. In this study we examined the leg muscle patterns at 3 time points as development of these spontaneous movements unfolds to determine if they exhibit attributes of locomotion reported in hatchlings. We also sought to determine whether the deeply flexed posture and movement constraint imposed by the shell wall modulate the muscle patterns.
Methodology/Principal Findings:
Synchronized electromyograms for leg muscles, force and video were recorded continuously from embryos while in their naturally flexed posture at embryonic day (E) 15, E18 and E20. We tested for effects of leg posture and constraint by removing shell wall anterior to the foot. Results indicated that by E18, burst onset time distinguished leg muscle synergists from antagonists across a 10-fold range in burst frequencies (1-10 Hz), and knee extensors from ankle extensors in patterns comparable to locomotion at hatching. However, burst durations did not scale with step cycle duration in any of the muscles recorded. Despite substantially larger leg movements after shell removal, the knee extensor was the only muscle to vary its activity, and extensor muscles often failed to participate. To further clarify if the repetitive movements are likely locomotor-related, we examined bilateral coordination of ankle muscles during repetitive movements at E20. In all cases ankle muscles exhibited a bias for left/right alternation.
Conclusions/Significance:
Collectively, the findings lead us to conclude that the repetitive leg movements in late stage embryos are locomotor-related and a fundamental link in the establishment of precocious locomotor skill. The potential importance of differences between embryonic and posthatching locomotion is discussed.
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