Neck Isometric Strength Dynamometer Protocol: 4-Direction Setup and Concussion-Risk Interpretation

An athletic trainer at a preseason football screening pulls out a handheld dynamometer, presses it against an athlete's forehead, says push, and writes down a number. Ten athletes later, three different staff members have rotated through the testing station, none of them anchoring the device the same way, none of them stabilizing the shoulders the same way, and the printout at the end of the day looks like four different tests got mixed into one spreadsheet. Nobody did anything wrong on purpose. The device just never came with a protocol, so everyone built their own.

That inconsistency matters more here than in most strength tests, because neck strength keeps showing up in the concussion-risk conversation for collision-sport athletes, and a number that moves 20% between testers is useless for flagging anyone. A standardized 4-direction isometric protocol fixes that: fixed body position, a fixed contact point per direction, a lever-arm measurement that turns raw force into a normalized index, and cutoffs that are actually built from the literature rather than eyeballed. None of it requires a machine-based cervical unit. A anchored load cell or a calibrated handheld dynamometer, a stabilization strap, and a tape measure get you there.

Why a Single Neck Strength Number Isn't Enough

Cervical musculature does not work as one muscle group with one strength value. Extension, flexion, and the two lateral flexion directions are driven by different muscle groups with different cross-sectional area and different mechanical leverage, and they rarely move together at the same rate when an athlete trains or detrains. An athlete who tests strong on extension because their sport rewards a bull-neck bracing pattern can still carry a real flexion or lateral flexion deficit that a single pooled neck strength score would bury completely.

That is the practical reason a proper protocol tests all four directions rather than one representative pull. It is also why raw force in kilograms or pounds is the wrong unit to compare across athletes. Two athletes can produce an identical 18kg reading on a handheld dynamometer and have meaningfully different actual neck strength, because one has a shorter head-to-contact-point lever arm than the other. Force alone ignores leverage; torque does not.

Equipment and Stabilization Setup

The test needs a way to record peak isometric force in a fixed position, a way to stop the trunk from doing the neck's job, and a way to measure the lever arm for each athlete.

Seat the athlete with the cervical spine in a neutral, slightly chin-tucked position, not extended and not flexed, before every trial. The stabilization strap across the chest and shoulders is not optional detail; without it, a strong athlete can generate a meaningful share of the recorded force by extending the trunk rather than the neck, and that substitution is the single biggest reason handheld neck testing produces inflated, unrepeatable numbers in untrained hands. Measure the lever arm once per athlete per direction, using the external auditory meatus (the ear canal opening) as the practical landmark for the cervical rotation axis, and record the straight-line distance in meters to the contact point. Reuse that measurement for every retest on that athlete rather than re-measuring casually each session, since small measurement drift compounds directly into the torque calculation below.

Step-by-Step 4-Direction Testing Protocol

1. General warm-up (3-5 minutes): Light cardio, neck circles, and controlled active range of motion through flexion, extension, and both lateral flexion directions.
2. Familiarization (1 trial per direction): One submaximal contraction at roughly 50% perceived effort per direction, in a fixed order: extension, flexion, left lateral flexion, right lateral flexion. Use the same order for every retest on that athlete.
3. Position and stabilize: Seat the athlete, apply the chest-shoulder strap, confirm neutral cervical alignment, and place the contact plate at the pre-measured landmark for the direction being tested.
4. Maximal trials (make test): The athlete ramps up to a true maximal contraction over 1-2 seconds and holds for 3-5 seconds against the fixed resistance while the examiner or device records peak force. Run 3 trials per direction with 30-45 seconds of rest between trials and 60-90 seconds between direction changes.
5. Valid trial criteria: Discard any trial where the stabilization strap visibly loosens, where the athlete's chin juts forward to recruit accessory muscle, or where the recorded curve shows a double peak rather than one clean ramp-and-hold.
6. Scoring: Record the highest valid trial per direction, not the average of three, since a single fatigue-affected trial can drag an average below true capacity.

Total time per athlete, including warm-up and all four directions, runs 8-10 minutes. For team-wide preseason screening, two testing stations working in parallel can move through a 40-athlete roster inside a single practice window.

Turning Force Readings Into Torque, NSI, and Ratios

Raw dynamometer force needs two conversions before it is comparable across athletes: turning force into torque using the lever arm, then normalizing torque to body mass.

Torque: T = F × d, where F is peak force in newtons and d is the lever arm distance in meters from the external auditory meatus to the contact point. If your dynamometer reads in kilograms-force, multiply by 9.81 to convert to newtons first.

Neck Strength Index: NSI = T / m, where m is body mass in kilograms, expressed in newton-meters per kilogram (Nm/kg). Normalizing this way keeps a heavier, larger-headed athlete from automatically outscoring a lighter athlete who is producing more torque relative to the mass their neck actually has to protect.

Worked example: an athlete produces 210N of peak extension force with a lever arm of 0.28m, giving 58.8Nm of torque. At a body mass of 82kg, extension NSI comes out to 0.72Nm/kg. The same athlete's flexion trial reads 145N at the same 0.28m lever arm, or 40.6Nm, giving a flexion NSI of 0.50Nm/kg.

From there, two ratios matter more than either raw number alone. Flexion-to-extension ratio (F:E) is flexion NSI divided by extension NSI, 0.50 / 0.72 = 0.69 in this example. Left-right symmetry index for the lateral flexion pair is the difference between sides divided by the stronger side, times 100: an athlete reading 0.61Nm/kg on the left and 0.55Nm/kg on the right posts (0.61-0.55)/0.61 × 100, roughly a 10% asymmetry, right at the edge of the flag threshold described below.

What the Research on Cervical Dynamometry Actually Shows

Leggett, Graves, Pollock, Shank, Carpenter, Holmes, and Fulton (1991), publishing in the American Journal of Sports Medicine, put the isometric 4-direction protocol on the map using a fixed cervical testing device on asymptomatic adults. The consistent pattern their data established, one still used to sanity-check field readings today, is that extension strength substantially exceeds flexion strength in the same athlete, driven by the larger cross-sectional area of the posterior cervical extensors compared to the anterior flexors. Their test-retest reliability across sessions came back strong enough to support repeated testing on the same protocol over a training block. The limitation worth carrying forward: their sample trained on a fixed machine with a controlled lever arm built into the device, not a handheld field dynamometer, so the exact numeric strength values do not transfer directly to a strap-and-load-cell field setup; the direction of the finding (extension well above flexion, high test-retest consistency) is what generalizes, not the raw torque figures.

Collins, Fletcher, Fields, Kluchurosky, Rohrkemper, Comstock, and Cantu (2014), in the Journal of Primary Prevention, applied a comparable 4-direction handheld dynamometer protocol to 6,704 high school athletes across 51 schools before their competitive seasons, then tracked diagnosed concussions through certified athletic trainers over the following year. Each one-pound increase in isometric neck strength was associated with roughly a 5% lower odds of sustaining a concussion that season. The limitation the authors themselves flagged is central to how this protocol should be used: strength was captured once, at a single preseason timepoint, in an observational cohort with no control group, so the finding is an association between baseline strength and later injury risk, not proof that strengthening the neck after a low baseline reading causes a drop in risk. A dynamometer reading is a risk-stratification input, not a diagnostic or a guarantee.

Normative Ranges and What to Flag

The bands below are built from the direction and reliability patterns established across the cervical dynamometry literature, expressed through the NSI calculation above. Use them to classify a profile and to decide what needs a training response, not as a pass-fail line separating cleared from not cleared.

An athlete sitting inside the trained range on every metric but showing a 14% lateral flexion asymmetry should not be waved through because the overall numbers look fine. The asymmetry is the actionable flag, and it is exactly the kind of finding a pooled single-number test would never surface.

Errors That Wreck a Neck Strength Reading

Using Results in a Concussion-Risk-Management Program

Treat a low or asymmetric NSI as one input into a broader preseason screening panel that already includes baseline balance and symptom-reporting tools, not as a standalone predictor and never as a return-to-play clearance test on its own. The Collins data supports flagging athletes with weaker baseline neck strength for a targeted correctives block, not benching anyone based on a single dynamometer session.

For athletes flagged on extension, flexion, or asymmetry, a 6-8 week corrective block built around 4-way isometric holds, progressing to manual or band resistance, and finishing with unanticipated perturbation drills tends to move the needle faster than generic neck exercises pulled from a warm-up sheet. Retest on the identical protocol, same chair, same lever arm measurement, same fixed order, at 6-8 weeks. An athlete who has not closed at least half the gap on a flagged metric by then is either under-dosing the corrective work or carrying a mobility or motor-control issue that needs individual attention beyond a group program. Keep the retest cadence consistent across a season; testing once in August and never again defeats the purpose of tracking a trainable, modifiable metric in the first place.