Monitoring Neuromuscular Performance in Military Personnel

Abstract

A necessarily high standard for physical readiness in tactical environments is often accompanied by high incidences of injury due to overaccumulations of neuromuscular fatigue (NMF). To account for instances of overtraining stimulated by NMF, close monitoring of neuromuscular performance is warranted. Previously validated tests, such as the countermovement jump, are useful means for monitoring performance adaptations, resiliency to fatigue, and risk for injury. Performing such tests on force plates provides an understanding of the movement strategy used to obtain the resulting outcome (e.g., jump height). Further, force plates afford numerous objective tests that are valid and reliable for monitoring upper and lower extremity muscular strength and power (thus sensitive to NMF) with less fatiguing and safer methods than traditional one-repetition maximum assessments. Force plates provide numerous software and testing application options that can be applied to military's training but, to be effective, requires the practitioners to have sufficient knowledge of their functions. Therefore, this review aims to explain the functions of force plate testing as well as current best practices for utilizing force plates in military settings and disseminate protocols for valid and reliable testing to collect key variables that translate to physical performance capacities.

Keywords: countermovement jump; drop jump; force plates; isometric-mid-thigh pull; military personnel; neuromuscular fatigue; soldiers; squat jump; tactical athletes.

Figure 1

Practical training scenario of soldiers jumping over and landing from obstacles in loaded (weighted vest) and unloaded conditions (A). The use of drop jump testing onto force plates; (B) to understand the amount of forces (Fz, vertical ground reaction forces, vGRFs; Fy, saggital plane; Fx, frontal plane) occurring during landing tasks. The appearance of U.S. Department of Defense (DoD) visual information does not imply or constitute DoD endorsement.

Figure 2

Practical operational scenario of soldiers jumping over a wall during training while under external loads (full kit) (A). The use of countermovement jump testing on force plates; (B) to (1) understand the amount of forces produced (Fz, vertical ground reaction forces, vGRFs; Fy, saggital plane; Fx, frontal plane); (2) estimate jump height, reactive strength capabilities, and power output; (3) compare performances under unloaded and loaded conditions for interpreting the ability to perform under external loads. The appearance of U.S. Department of Defense (DoD) visual information does not imply or constitute DoD endorsement.

Figure 3

This is an example of a force-time curve from a countermovement jump (CMJ). The weighing phase occurs for at least one second prior to initializing movement (point A). The individual begins descent (i.e., eccentric action) resulting in an initial drop in the forces, known as the unweighting phase, until bodyweight is reached (point B). The individual must decelerate through the remainder of the eccentric phase until velocity reaches zero (point C), known as the braking phase. The individual then explodes upwards until take-off (point D), reaching maximal jump height approximately half way through the flight phase (point E), and eventually landing (point F). The landing phase then begins until a stabilization period is reached (point G).

Figure 4

This is an example the force-time curve from a drop jump (DJ). The weighing phase still occurs for at least one second, but does not include capturing the individuals bodyweight. The individual begins the drop jump by stepping off, not jumping from or stepping down from, a standard height (point A) until coming into first contact with the ground (point B) and beginning the eccentric (i.e., braking) portion of the initial landing phase until velocity reaches zero (point C). As quickly as possible, the individual then explodes upwards until take-off (point D), reaching maximal jump height approximately half way through the flight phase (point E), and eventually landing (point F). The landing phase begins until a stabilization period is eventually reached (point G).

Figure 5

A correct example of a force-time curve from an isometric mid-thigh pull (IMTP) is presented in (A) including a one second weighing phase (point A). Example variables of interest may exist in time epochs from 0 (initiation of movement, (point B) to 250 milliseconds (point C), such as the slope of the force-time curve (point D) or the area under the force-time curve, known as impulse (point E). Additionally, peak force (point F) is calculated and often most reliable. In (B), common errors in assessing the IMTP are presented, such as too much movement during the weighting phase (point A) and a countermovement prior to pulling on the bar (point B).