1. Patient baseline data
2. Recorded Latencies in the Study (Optional - For Deviation/%)
Results
| Nerve | 1. Regression (Mean | Maximum) |
Desvio Obs. (Dif ms | %) |
2. Stålberg (Maximum) |
3. Table (Min | Mean | Max) |
|---|---|---|---|---|
| F - Median | -- | -- | -- | -- | N/A |
| F - Ulnar | -- | -- | -- | -- | -- | -- | -- |
| F - Fibular | -- | -- | -- | -- | N/A |
| F - Tibial | -- | -- | -- | -- | -- | -- | -- |
| H - Tibial | -- | -- | -- | -- | N/A |
| H - Median | -- | -- | -- | -- | N/A |
| Dif. Ulnar Corr. | -- | |||
| Assimetria H (Dir/Esq) | -- | |||
Height-Based Reference Tables
F wave - Ulnar
| Height (m) | F min (ms) | F mean (ms) | F max (ms) |
|---|---|---|---|
| 1.50 | 26.0 | 27.5 | 30.0 |
| 1.55 | 26.5 | 28.0 | 30.5 |
| 1.60 | 27.0 | 29.0 | 31.5 |
| 1.65 | 28.0 | 30.0 | 32.5 |
| 1.70 | 29.0 | 31.0 | 33.5 |
| 1.75 | 30.0 | 31.5 | 34.0 |
| 1.80 | 30.5 | 32.5 | 35.0 |
| 1.85 | 31.0 | 33.5 | 36.0 |
| 1.90 | 32.0 | 34.5 | 37.0 |
F wave - Tibial
| Height (m) | F min (ms) | F mean (ms) | F max (ms) |
|---|---|---|---|
| 1.50 | 44.5 | 47.5 | 51.0 |
| 1.55 | 46.0 | 48.5 | 52.5 |
| 1.60 | 47.5 | 50.5 | 54.0 |
| 1.65 | 49.0 | 52.0 | 56.0 |
| 1.70 | 51.0 | 54.0 | 58.0 |
| 1.75 | 53.0 | 56.0 | 60.0 |
| 1.80 | 55.0 | 58.0 | 61.5 |
| 1.85 | 57.0 | 60.0 | 63.0 |
| 1.90 | 58.5 | 62.0 | 65.0 |
F-wave and H-reflex latencies
The F-wave assesses proximal motor pathways; the H-reflex assesses the Ia reflex arc. Compare to age regression (Stålberg/Johnson) or height tables for ulnar and tibial nerves.
The F wave is a late response generated by antidromic activation of alpha motor neurons. It assesses the proximal motor nerve segment (roots, plexus) and is especially useful when prolonged in multiple nerves, suggesting polyradiculopathy or CIDP. F-wave latency should be compared with expected latency for patient height and age.
The H reflex is the electrophysiological equivalent of the Achilles reflex: the Ia sensory stimulus travels via the tibial nerve to the cord (S1), where it synapses with motor neurons generating the H wave. It is prolonged or absent in S1 radiculopathy and sensorimotor polyneuropathies. R/L H asymmetry > 1.8 ms is significant.
Three reference methods are available:
1. Regression (mean | max): linear equation with height and age; provides expected latency and maximum limit.
2. Stålberg (max): Stålberg and Falck formula - maximum F-wave latency.
3. Table (min | mean | max): tabulated reference values by height (ulnar and tibial).
References:
· Stalberg E, Falck B. The role of electromyography in neurology. Electroencephalogr Clin Neurophysiol 1997;103(1):3–10.
· Bischoff C et al. Electrophysiology of distal neuropathies. Clin Neurophysiol 2004;115(11):2520–2529. doi: 10.1016/j.clinph.2004.05.011
F-wave physiology
The F-wave results from antidromic activation of a subset of alpha motoneurons — the impulse travels proximally to the root, reflects and returns as a late potential. It assesses the proximal segment (root, plexus) of median, ulnar, tibial and peroneal nerves. Minimum F latency is the most reproducible parameter. Prolongation in multiple nerves supports proximal demyelination in CIDP (EAN/PNS 2021).
H-reflex physiology
The H-reflex is the electrophysiologic analog of the stretch reflex: Ia afferent → interneuron → alpha motoneuron → H response (before direct CMAP). Tibial H assesses the S1 arc; median H assesses C6–C7. Interside H asymmetry > 1.8 ms (tibial) is abnormal. Absent H with preserved CMAP suggests arc lesion or severe polyneuropathy.
Available reference methods
- Regression (Mean | Max): linear equation with height and age.
- Stålberg (Max): classic formula for maximum F latency.
- Height table: Min | Mean | Max for ulnar and tibial.
Pitfalls and clinical correlation
- Submaximal stimulation: absent F from technique, not pathology.
- Advanced age: mild F prolongation — use age regression.
- Severe CTS: prolonged median F from distal demyelination.
- Isolated radiculopathy: abnormal F or H in affected nerve; EMG confirms segmental denervation.
Frequently asked questions
Does prolonged F-wave indicate radiculopathy?
Minimum F-wave delay may indicate proximal involvement (root, plexus) or proximal demyelination.
How to use height tables for F-wave?
Expected ulnar and tibial latencies vary with stature; this calculator applies Stålberg/Johnson references.