Certain parameters that have been used for a long time in quantifying induced isokinetic fatigue were put to test and challenged in this Belgian-French collaborative study. Although the reported low reproducibility renders some of these parameters invalid, this result holds only when applying the specific testing protocol (concentric only, knee muscles) used in this study. Whether this applies to different fatigue protocols and other muscle groups requires thorough research.
Prof. Dvir's Commentary:
Isokinetic dynamometry is widely regarded as the gold standard for muscle strength testing. Its use in this respect has been described in thousands of papers that have looked into various muscle groups, contraction modes, angular velocities etc. However, employing this technology for assessing fatigability has gained much smaller attention among researchers reflecting largely non-standardized protocols and involvement of other factors that are less likely to affect the measurement of strength.
This outcome has much has to do with the main subject, literally speaking, of the test: the human subject. As pointed out by the authors of this important and comprehensive Belgian-French study, 'the subject’s motivation and/or the arduousness of the fatigability [during the] testing session can potentially account for the increasing variability during the evaluation [as each consecutive contraction from the first to the last] must be achieved with maximal intensity over the entire ROM'. Such effort may adversely affect the subject's ability to maintain maximal contraction due to discomfort or other distracting factors, even though the motivation for maximizing the effort is firmly there.
To explore the stability of fatigability indices, the authors have used reciprocal concentric contractions of the knee extensors and flexors, arguably the most researched antagonist couple in the human body. The peak moment (PM) and maximal work (MW) of each muscle group served as outcome measures, underlying the slightly different role of each. The stability of the findings was examined in healthy participants, over 3 testing sessions, in terms of the reproducibility of a group of 54 variables. Among the 54, a small number were directly measured whereas the majority of the variables were obtained as ratios of given variables within the group (referred to as the 'derived').
The importance of analyzing reproducibility in quantitative terms cannot be overstated. It is a critical step in ascertaining the valid use of any outcome measure and those associated with isokinetic testing are no outsiders. In addition, cutoffs for meaningful changes (SRD, MDC etc.) are possibly the most significant outcome of such an analysis. It transpires that within the confines of the study, the ratio-based ('derived') indices of either muscle group, should not be used in assessing their fatigability. Furthermore, applying the direct (measured) indices, should be reserved to analyzing the fatigue of the quadriceps, exclusively.
Is that the end of isokinetic fatigue analysis of the hamstring ? The authors concede that concentric maximal repetitive activity is not an habitual function of this muscles and therefore leave the door open for a study focusing e.g. on eccentric action of this muscle group. It may also be the case that the angular velocity used in this study was not ideal for this particular objective, while the use of reciprocal vs. single muscle single contraction mode testing could also confound the picture and is therefore worth studying.
On the other hand, inasmuch as the specific protocol described in this study is applied in future studies, one should be extremely careful in drawing any conclusions regarding fatigability of either the extensors or flexors of the knee.
Paulus J, Bosquet L, Forthomme B, Donneaud A-F, Grémeaux V, Croisier J-L. Measured and derived parameters of isokinetic fatigability of knee muscles: What can we apply, what should we not? Isokinetics and Exercise Science 27(1), 2019
Paper of the Month - the initiative
The main objective of the PoM initiative is to serve as an update forum for users of isokinetic dynamometry. Recent papers, generally of the last 3 preceding months, relating to this technology and its applications will be reviewed regularly by Prof. Zeevi Dvir, who will select those that in his opinion present an important/relevant contribution to the science of isokinetic testing and conditioning. The selection will consider the novelty, scientific rigor and possible applicability of the study without any prejudice, reflecting PHYSIOMED's commitment to the highest standards the company stands for as a world leader in isokinetic technology.
Based at the Dept. of Physical Therapy, the Sackler Faculty of Medicine, Tel Aviv University, Prof. Dvir serves also as a Non-teaching Adjunct Professor at the Biomechanics and Ergonomics Lab, School of Kinesiology and Health Studies (SKHS), Queen's University, Canada.
Prof Dvir is an international leader in isokinetics. He is the author of the widely recognized leading title in the field "Isokinetics: Muscle Testing, Interpretation and Clinical Applications" (Churchill Livingstone, 1st ed., 1995; Elsevier 2nd ed., 2004). He is also the Editor-in-Chief of Isokinetics and Exercise Science (IOS Press, Amsterdam, Holland) since 1998, the only international journal dedicated to the science and practical aspects of this technology. Prof. Dvir has published more than 60 papers on isokinetics. He coined the terms Dynamic Control Ratio (DCR), which is also known as the functional ratio. The DCR has mostly been applied in the context of muscular balance around the knee especially with respect to ACL deficiency and reconstruction and is expressed as the ratio: Hecc/Qcon. Prof. Dvir was also the first to describe the DCE (the Difference between the high and low velocity Ecc/Con ratios) to assess submaximal effort, a core concept in medicolegal analysis of muscular weakness. A US patent he owns paved the way to a series of papers describing the utilization of Short Range of Motion isokinetic testing and conditioning.