Table 1

Data yielded from the IMTP and CMJ when using portable force plate technology

The isometric mid-thigh pull (IMTP) test
Currently, the IMTP is used as part of the role fitness test (RFT) at entry and end of basic training. However, due to limitations with existing testing equipment (use of weighing scales), peak force (measured in kg) is the only output derived from the IMTP test used within the Army physical employment standards. When measured using portable force plates (Hawkin Dynamics), the IMTP (figure 1) is a test that can assess multiple derivatives of maximal lower-limb muscle force production capability.
Current British Army/DMS capabilityProposed future British Army/DMS capability
  • Peak force production (measured in kg)

  • Peak Force (measured in Newtons (N), and easily converted to kg)

  • Relative peak force (N/kg)

  • Force at 150 ms, 200 ms and 250 ms

  • RFD measured across specific epochs (ie, 0–150 ms, 0–200 ms, 0–250 ms)

  • Relative RFD measured across specific epochs

  • Limb asymmetry

The CMJ can yield valuable insight into an individual’s neuromuscular function, ballistic force production capability and stretch-shortening cycle (SSC) capabilities,11 and greater insight into an individual’s capacity to accelerate their body mass. The CMJ has been shown to be a valid and reliable measure of rapid lower-body force production18 yet it is quick to perform, non-fatiguing and requires minimal familiarisation. Comprehensive insights into neuromuscular function can be gained through detailed analyses of force-time curves throughout specific phases19 or the entire CMJ,11 when compared with measuring the output of the jump alone (ie, jump height). Six key CMJ phases can be identified from force-time curves including: weighing, unweighting, braking, propulsion, flight and landing.
Combining the IMTP and CMJ will enable the calculation of the participant’s DSI. The DSI is the ratio between peak isometric force produced (using the IMTP) versus how much of that force can be produced during a ballistic movement (using the CMJ).20 This enables the profiling of an individual’s ‘strength potential’ and how much of this potential is being used during high-speed ballistic movements (eg, sprinting/jumping) which are essential attributes when performing physically arduous military-specific tasks.7
Current British Army/DMS capabilityProposed future British Army/DMS capability
  • Jump height

  • Jump height

  • Time to take off

  • (modified) Reactive Strength Index

  • Propulsive phase duration

  • Mean and peak propulsive force

  • Limb asymmetry

  • CMJ, countermovement jump; DMS, Defence Medical Services; DSI, Dynamic Strength Index; IMTP, isometric mid-thigh pull; RFD, rate of force development.