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.
Highlights
Assessment of human maximal muscular strength and power ability is routinely performed within strength and conditioning (McMaster et al, 2014; Paul and Nassis, 2015; Suchomel et al, 2016), as well as physical therapy and rehabilitation practice (Dickoff-Hoffman and Davies, 1993; Myer et al, 2006)
If multiple methods were used in a study, we considered the results obtained by the method that we judged to be the more reliable and valid
We focus on the data grouped into the aforementioned three categories based on the knee angle
Summary
Assessment of human maximal muscular strength and power ability is routinely performed within strength and conditioning (McMaster et al, 2014; Paul and Nassis, 2015; Suchomel et al, 2016), as well as physical therapy and rehabilitation practice (Dickoff-Hoffman and Davies, 1993; Myer et al, 2006). During the rehabilitation of the anterior cruciate ligament injury, it is common to perform both single-joint knee strength assessment and jump or hop tests for height or distance (a multi-joint task; O’Malley et al, 2018). In terms of single-joint strength assessments, most of the research has been dedicated to the knee joint, which is likely due to the high reliability of these measurements and their implications in rehabilitation (de Araujo Ribeiro Alvares et al, 2015; Muñoz-Bermejo et al, 2019) and implications in the rehabilitation of several prevalent and detrimental lower-limb injuries (Myer et al, 2006; Cvjetkovic et al, 2015; Kaeding et al, 2017; Bourne et al, 2018; Goff et al, 2018; O’Malley et al, 2018). Moderate to high reliability and validity have been reported for knee strength assessments performed by handheld dynamometers (Mentiplay et al, 2015; Chamorro et al, 2017; Chopp-Hurley et al, 2019; Lesnak et al, 2019; van der Made et al, 2019)
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