Research Summary: Methodological considerations for HHD and portable fixed frame isometric hip and groin strength testing

Brief Summary

Practitioners frequently measure the strength of athletes to understand better performance parameters and factors that may impact injury risk. The validity and reliability of the tools and protocols practitioners employ are fundamental to the outcomes of these efforts.

Hip and groin injuries contribute to between 2 and 5% of all sporting injuries (Morelli and Smith, 2001). While isokinetic devices have long been considered the "gold standard" in measuring hip and groin strength (Weir et al., 2015), these devices are costly, time-consuming to use, and often not sufficiently portable to meet team needs. As a result, more practical and time-efficient hand-held and fixed-frame dynamometry devices have been explored and, when used appropriately, found to be reliable force-measuring devices.

The current study compared hand-held (HHD) and a portable fixed-frame dynamometry (KT360) systems in an attempt to establish the concurrent validity when assessing short-lever isometric hip and groin strength. Within-method differences, including the use of average and maximum peak force, their interchangeability, the minimum number of repeat trials, and between-method differences, were explored.

Thirty-three recreationally active individuals were assessed. Participants were randomly assigned to either the KT360 or the HHD. Bilateral testing of the Adductors and Abductors was performed on the KT360 utilizing a supine short-lever test in 90 degrees of knee flexion and 45 degrees of hip flexion. Conversely, unilateral testing was performed using the HHD with patients positioned in the same degrees of hip and knee flexion (see Figure 1). Each protocol was performed three times, with each isometric repetition lasting 5s and 30s rest afforded between repetitions.

Figure 1

Note 2 factors that compromise the validity of the HHD protocols employed. A. the relative lack of stabilization of the contralateral limb/pelvis in the HHD protocols. This precludes eliciting a true maximum voluntary Isometric Contraction (MVIC) of the hip adductors and/or abductors. B. The therapist's position and strength are unlikely to provide sufficient fixation of the HHD and contribute further to the invalid measurement of hip MVIC.


The main findings reported were:

  • Excellent ICC values (0.89-0.97)
  • SEM% (0.59-2.26) demonstrating minimal error
  • MDC for HHD (2.17-3.56) KT360(1.63-6.26) with the highest MDC value for the Adductor groups
  • The KT360 produced significantly larger forces using the bilateral testing method than the HHD unilateral testing method, with substantial average increases of 94.6-101.2% and percentage increases from 11.2-247.5%

The authors report excellent reliability for both technologies but significantly higher strength results for KT360. They further suggest these results are a product of the bilateral facilitation effect. However, the authors have not addressed the issue of validity when using the HHD in the protocol utilized. 

While the HHD may be reliable, it is unable to provide an accurate measurement of hip adductor or abductor muscle MVIC in this position due to a lack of adequate stabilization of the contralateral limb/pelvis and fixation of the dynamometer when testing in the supine position. 

KT360 reliably elicited significantly higher / true MVIC results. Moreover, this KT360 is not due to a 'bilateral facilitation effect' as the authors suggest, which may be a valid point but does not consider all factors. Still, rather, It is a more valid protocol that utilizes a =n adequately stiff/quality frame that ensures both stability and mitigates force leakage. The limitation of this article is that it fails to identify the differences in athlete stabilization between the two protocols used for testing. Future comparisons between HHD and fixed frame isometric testing devices should review the validity of testing with adequate athlete stabilization and the effects of subsequent force production when testing isometrically.

To access the article, please click here.

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