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Review
. 2021 Oct 15:12:767941.
doi: 10.3389/fphys.2021.767941. eCollection 2021.

Establishing Reference Values for Isometric Knee Extension and Flexion Strength

Nejc Šarabon  1   2   3   4 , Žiga Kozinc  1   2 , Mihael Perman  5   6
Affiliations
Review

Establishing Reference Values for Isometric Knee Extension and Flexion Strength

Nejc Šarabon et al. Front Physiol. .

Abstract

Single-joint isometric and isokinetic knee strength assessment plays an important role in strength and conditioning, physical therapy, and rehabilitation. The literature, however, lacks absolute reference values. We systematically reviewed the available studies that assessed isometric knee strength. Two scientific databases (PubMed and PEDro) were searched for the papers that are published from the inception of the field to the end of 2019. We included studies that involved participants of both genders and different age groups, regardless of the study design, that involved isometric knee extension and/or flexion measurement. The extracted data were converted to body-mass-normalized values. Moreover, the data were grouped according to the knee angle condition (extended, mid-range, and flexed). A meta-analysis was performed on 13,893 participants from 411 studies. In adult healthy males, the pooled 95% confidence intervals (CI) for knee extension were 1.34-2.23Nm/kg for extended knee angle, 2.92-3.45Nm/kg for mid-range knee angle, and 2.50-3.06Nm/kg for flexed knee angle, while the CIs for flexion were 0.85-1.20, 1.15-1.62, and 0.96-1.54Nm/kg, respectively. Adult females consistently showed lower strength than adult male subgroups (e.g., the CIs for knee extension were 1.01-1.50, 2.08-2.74, and 2.04-2.71Nm/kg for extended, mid-range, and flexed knee angle condition). Older adults consistently showed lower values than adults (e.g., pooled CIs for mid-range knee angle were 1.74-2.16Nm/kg (male) and 1.40-1.64Nm/kg (female) for extension, and 0.69-0.89Nm/kg (male) and 0.46-0.81Nm/kg (female) for flexion). Reliable normative for athletes could not be calculated due to limited number of studies for individual sports.

Keywords: knee strength; lower limb; muscle capacity; normative; reference values.

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Conflict of interest statement

NS was employed by company S2P, Science to Practice, Ltd. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. Authors alone are responsible for conceptualization of the study and data analysis. The funders provided part of the authors’ salaries through national research fund and were not involved in any part of the study.

Figures

Figure 1
Figure 1
Flowchart of the study selection process. *Note that the numbers of the excluded papers by each reason do not add up to the total, as two papers were excluded for more than one reason.
Figure 2
Figure 2
Pooled mean strength values with 95% confidence intervals for adult and elderly non-athlete populations (separated by knee angle).
Figure 3
Figure 3
Pooled mean strength values with 95% confidence intervals for adult non-athlete populations across knee angle conditions.
See this image and copyright information in PMC

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