The amplitude of the Achilles tendon reflex in infants is related to body position

Area of Science:

• Neuroscience
• Developmental Biology
• Pediatrics

Background:

• The Achilles tendon reflex (ATR) is a fundamental neurological response.
• Understanding infant motor development and reflex modulation is crucial for assessing neurological health.
• Body position may influence the expression of neonatal reflexes.

Purpose of the Study:

• To investigate the effect of body position (prone vs. supine) on the Achilles tendon reflex (ATR) in healthy infants.
• To compare the ATR's clinical and neurophysiological responses across different infant ages and positions.

Main Methods:

• Clinical assessment of ATR by visual inspection of ankle plantar flexor muscle contraction following tendon taps.
• Electromyographic (EMG) recordings of gastrocnemius muscle activity to measure ATR amplitude and latency.
• Infants were tested in both prone and supine positions at multiple time points: postnatal day 1, 2, 3, and 6 months.

Main Results:

• At postnatal day 1, the ATR was significantly more frequent in the prone position (88%) than in the supine position (25%).
• From 2 months onwards, the frequency of positive ATRs did not differ significantly between prone and supine positions.
• At 6 months, EMG recordings revealed a significantly higher ATR amplitude in the prone position compared to the supine position.

Conclusions:

• The Achilles tendon reflex in healthy infants is modulated by body position, being more pronounced in the prone position.
• This positional effect is evident in both clinical assessments and neurophysiological measurements.
• The findings provide insights into the developmental trajectory of motor control and reflex modulation in infants.