What factor is critical in determining the frequency used for sensory-level TENS compared to motor-level TENS?

In the context of sensory-level transcutaneous electrical nerve stimulation (TENS) versus motor-level TENS, the critical factor distinguishing their frequency is that sensory-level TENS is designed to operate below the motor threshold. This means that the stimulation used in sensory-level TENS should activate sensory nerves to alleviate pain without eliciting muscle contractions, which require a higher frequency to reach the motor threshold.

The ability to stay under the motor threshold is essential as it allows for the modulation of pain through the activation of the ascending pain control pathways without inducing muscle responses. This is particularly beneficial in managing acute pain and can provide immediate relief, as it activates the gate control theory of pain by stimulating A-beta fibers that inhibit pain transmission through the spinal pathways.

While other factors like patient condition and individual responses can influence settings, the fundamental principle that the frequency must be below the motor threshold remains the primary determinant in choosing the appropriate frequency for sensory-level TENS.