The de qi, or needling sensation as we refer to it in medical Acupuncture is not a single, but rather a combined sensory response which occurs when a variety of sensory receptors are stimulated.
These would include small fibre innervated nociceptors and myelinated fibre innervated mechanoreceptors (Leung et al, 2006).
Zhang et al (2012) hypothesise that the numbness, heaviness and distension felt as part of the needle sensation may be due to the stimulation of sites rich in muscle spindles and tendon organs (proprioceptors) and the soreness and aching in the deep tissues is likely to be due to the activation of intramuscular nociceptors (type II/III).
Kong et al (2009) found a relationship between acupuncture analgesia and the sensation of numbness and soreness on needling, but not for other sensations commonly associated with de qi. This would suggest that perhaps both types of receptors described above may need to be activated in order to bring about analgesia. However we should be careful not overstimulate the nociceptive C fibres in skin and muscle (referred to as type IV) and bring about excessive pain on while needling otherwise we could have an adverse effect.