Recruitment

1. What is the rule of 5's for recruitment?
2. What is the difference between the recruitment frequency (RF) and the recruitment interval (RI)?
3. What is the RF and RI in a neuropathic process?
4. What is the RF and RI in a myopathic process?
5. What is the recruitment ratio (RR)?

Answers:
1. The first MUAP starts firing at a frequency of 5Hz. The second MUAP comes in at 10Hz and should be firing at 5Hz. A third MUAP comes in when the first is firing at 15Hz and the second at 10Hz. A fourth MUAP comes in when the first is firing at 20Hz.
2. The RF is the frequency of the first MUAP when a second begins to fire. Normal is <20Hz. The RI is the interval (measured in ms) between two discharges of the same MUAP when a second begins to fire. Normal is 100ms.
3. A neuropathic process has an increased RF and decreased RI.
4. A myopathic process has a decreased RF and an increased RI.
5. RR is calculated as the FR of the first MUAP divided by the number of MUAPs on the screen. Normal RR is <10.