Abstract
“Flexibility” tests are traditionally performed voluntarily relaxed by rotating a joint slowly; however, functional activities are performed rapidly with voluntary/reflexive muscle activity. Here, we describe the reliabilities and differences in maximum ankle range of motion (ROMmax) and plantar flexor mechanical properties at several velocities and levels of voluntary force from a new test protocol on a commercially available dynamometer. Fifteen participants had their ankle joint dorsiflexed at 5, 30, and 60° s−1 in two conditions: voluntarily relaxed and while producing 40% and 60% of maximal eccentric torque. Commonly reported variables describing ROMmax and resistance to stretch were subsequently calculated from torque and angle data. Absolute (coefficient of variation (CV%) and typical error) and relative (ICC2,1) reliabilities were determined across two testing days (≥72 h). ROMmax relative reliability was good in voluntarily relaxed tests at 30 and 60° s−1 and moderate at 5° s−1, despite CVs ≤ 10% for all velocities. Tests performed with voluntary muscle activity were only reliable when performed at 5° s−1, and ROMmax reliability was moderate and CV ≤ 8%. For most variables, the rank order of participants differed between the slow‐velocity, relaxed test, and those performed at faster speeds or with voluntary activation, indicating different information. A person's flexibility status during voluntarily relaxed fast or active stretches tended to differ from their status in the traditional voluntarily relaxed, slow‐velocity test. Thus, “flexibility” tests should be completed under conditions of different stretch velocity and levels of muscle force production, and clinicians and researchers should consider the slightly larger between‐day variability from slow‐velocity voluntarily relaxed tests.
Highlights
IntroductionMaximal joint range of motion (ROMmax) and resistance to tissue elongation are important physical characteristics that influence an individual's ability to perform movements of daily living or sporting tasks.[1,2] these characteristics are sometimes associated with muscle strain injury risk.[3,4] From a functional perspective, a lesser antagonist muscle resistance resulting from a high muscle compliance should allow for the performance of agonist muscle actions at lower energetic/metabolic cost compared to cases in which the antagonist is stiffer.[2,5] Given the functionalScand J Med Sci Sports. 2021;31:1009–1025. | wileyonlinelibrary.com/journal/sms 1009| 1010 importance of both ROM and resistance to tissue elongation as well as the apparent changes that occur with aging,[6,7] disease,[8,9] and disuse[10,11] as well as muscle stretching and strength training interventions,10,12-14 it is not surprising that tests of both ROMmax and resistance to tissue elongation are included in clinical and applied settings.In research (and some clinical situations), flexibility tests are commonly performed using isokinetic dynamometers to rotate a joint at a low velocity, e.g. ≤5° s−1, and without voluntary activation of the muscle ( reflexive activity may be present) in order to determine ROMmax and to quantify passive musculo-articular complex (MAC) mechanical properties.[15]
Spearman's correlation analysis revealed significant positive moderate-to-strong correlations between ROMmax obtained in passive and 40-Ecc active stretching tests performed at 5° s−1, but a correlation was not observed in ROMmax in passive and 60-Ecc active stretching tests
The results showed that passive stretch tests could be performed at greater speeds than previously reported with relative reliability ranging from moderate to good based on intra-class correlation coefficients (ICCs)
Summary
Maximal joint range of motion (ROMmax) and resistance to tissue elongation are important physical characteristics that influence an individual's ability to perform movements of daily living or sporting tasks.[1,2] these characteristics are sometimes associated with muscle strain injury risk.[3,4] From a functional perspective, a lesser antagonist muscle resistance resulting from a high muscle compliance should allow for the performance of agonist muscle actions at lower energetic/metabolic cost compared to cases in which the antagonist is stiffer.[2,5] Given the functionalScand J Med Sci Sports. 2021;31:1009–1025. | wileyonlinelibrary.com/journal/sms 1009| 1010 importance of both ROM and resistance to tissue elongation as well as the apparent changes that occur with aging,[6,7] disease,[8,9] and disuse[10,11] as well as muscle stretching and strength training interventions,10,12-14 it is not surprising that tests of both ROMmax and resistance to tissue elongation are included in clinical and applied settings.In research (and some clinical situations), flexibility tests are commonly performed using isokinetic dynamometers to rotate a joint at a low velocity, e.g. ≤5° s−1, and without voluntary activation of the muscle ( reflexive activity may be present) in order to determine ROMmax and to quantify passive musculo-articular complex (MAC) mechanical properties.[15]. ≤5° s−1, and without voluntary activation of the muscle ( reflexive activity may be present) in order to determine ROMmax and to quantify passive musculo-articular complex (MAC) mechanical properties.[15] The slow movement velocity used in the test is justified under the assumptions that (a) tonic/stretch reflexes are not evoked and do not influence ROMmax and/or the passive elastic properties of the MAC, and (b) results are not likely to be influenced by viscous properties of the muscle or tendon, which are strain rate-dependent.14-19 From a mechanistic perspective, this would allow discrimination between several neural and non-neural mechanisms underpinning ROM assessment.[20] both the slow velocity of the test and the lack of voluntary (and usually reflexive) muscle activity may reduce its functional relevance to activities of daily living or sporting tasks, which are performed at faster joint rotation velocities and usually under the influence of reflexive and/or voluntary muscle activity.[21,22] Such tests would be important from a clinical viewpoint, for people with neurological conditions (eg, spasticity, contracture) who may exhibit persistent ongoing muscle activity during activities of daily living
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