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. 2025 Feb 8;30(2):e70034. doi: 10.1002/pri.70034

Using Isometric Squat Strength to Predict Concentric and Eccentric Squat Strength in Young and Older Adults

Michael T Dunn 1,2, Phuong T M Quach 1, Monica McGraw 1, Richard I Preus 1,3, Robert C Barefoot 1,3, Winston C Lancaster 1, Jennifer Ponder 4, Harshvardhan Singh 2,5,✉
PMCID: PMC11806937  PMID: 39921916

ABSTRACT

Background

Resistive squat exercise is a well‐established technique to enhance the strength of muscles and bones of the back extensors in humans. Rehabilitation programs aimed at strengthening the muscles and bone of the back require the knowledge of the patient's 1 repetition maximum (RM) of squat exercise. Finding the 1RM value of squat exercise could lead to injury or seem nonfeasible because of the higher weights involved, especially in older adults.

Purpose

To investigate the predictive relationship between the maximum voluntary isometric squat strength and the 1RM concentric and eccentric squat strength in young and older individuals.

Methods

In our cross‐sectional study, individuals from two age populations, 21–35 years (young) and 55–75 years (older) were recruited and participated in two visits within a two‐week period. Our main outcome measures were: Maximum voluntary isometric squat strength (IsoMax) and 1RM of concentric (ConMax) and eccentric (EccMax) back squat strength were calculated for young and older adults. All the strength measures were normalized for body weight.

Results

IsoMax was a significant predictor of the ConMax (p = 0.003; Normalized ConMax = 0.708 + 1.376(Normalized IsoMax); 95%CI: 0.583–2.169) and EccMax (p = 0.003, Normalized EccMax = 0.844 + 1.433(Normalized IsoMax); 95%CI = 0.582–2.284) in older adults only. There was a trend toward significance for the relationship between IsoMax and ConMax (p = 0.058) in young adults.

Discussion

Our novel findings show that safe techniques for muscle strength assessment, such as maximum voluntary isometric squat strength, can be utilized in older populations to predict their 1RM of concentric and eccentric squat strength. Our novel equations provide the information necessary for designing effective rehabilitation regimes for strengthening the muscles and bone of the back in older adults.

Keywords: aging, loading, muscle, spine

1. Introduction

Squatting is one of the basic movements which is critical for performing activities of daily living as well as leisure‐time activities (Myer at al. 2014). The act of lifting and lowering a load against a resistance in a squat position, also known as resistive squat exercise, is utilized in rehabilitation programs to create anabolic stimulus on the muscles and bones of the vertebral column and lower limbs of the body (Wilk et al. 2018). Typically, designing resistive exercise programs for specific muscles during specific movements requires testing for the one repetition maximum (1RM) strength for the corresponding muscle performing the specific movement. For example, the 1RM of the squat exercise is the highest amount of weight one can lift and lower during a squat in a single repetition (Schoenfeld et al. 2021; Blazevich, Gill, and Newton 2002; Cormie et al. 2007). In healthy populations, the 1RM can be found by having an individual perform one repetition squat with increasing loads until they fail to lift and thus achieve their 1RM. The 1RM of the squat exercise is a reliable test in trained and untrained young adults (Mccurdy et al. 2004; Grgic et al. 2020). However, various clinical populations such as older adults with clinical conditions affecting the spine, such as osteoporosis, may be highly susceptible to injury because of the high load nature of the load being lifted (Braith et al. 1993; Shaw, McCully, and Posner 1995; Shirado et al. 1995). Notably, there are increasing reports of early onset of osteopenia or osteoporosis in young adults (Salari et al. 2021). Thus, young adults with conditions such as osteoporosis may also be at an increased risk for spinal injury because of the high load nature of the load being lifted during 1RM determination. Thus, there is a specific critical need to design novel ways to test the 1RM of the squat exercise in young adults and older adults with musculoskeletal conditions affecting the spine. A safe way to assess 1RM could help design scientifically effective rehabilitation programs to strengthen the spine in young adults and older adults with musculoskeletal conditions.

The squatting movement can be broken down into three distinct phases, with each phase corresponding to unique muscular contraction types. The large back muscles that are activated during loaded squat are the erector spinae muscle group, consisting of the iliocostalis, longissimus, and spinalis. The unique muscular contraction types of the erector spinae group that occur at different phases of the squatting movement are as follows: eccentric (muscle lengthening) contractions during the lowering phase, concentric (muscle shortening) contractions during the rising phase, and isometric (minimal to no change in muscle length) contractions occurring between the end of the lowering phase and the start of the rising phase of the squat. Typically, isometric contractions versus concentric and eccentric contractions have the lowest risk for movement‐related injury, and thus have been widely used in clinical settings as a means of measuring the force generation capabilities of muscle groups (Lum, Haff, and Barbosa 2020). Previous studies have demonstrated that the maximum voluntary isometric squat strength can predict the free barbell squat 1RM in young individuals of both the sexes (Blazevich, Gill, and Newton 2002; Petrović et al. 2020; Parai 2016). The diagnostic and prognostic values of the maximum voluntary isometric squat contractions are further underpinned by their utility to quantify the effectiveness of back strengthening rehabilitation programs while also being less fatiguing and easier to perform than concentric or eccentric contractions (Warneke et al. 2023; Drake, Kennedy, and Wallce. 2018).

The 1RM concentric strength is the main determinant of the conventional 1RM testing because it involves testing a muscle for the maximum amount of load it can lift. The 1RM value thus obtained is utilized to design a progressive resistive squat exercise program for musculoskeletal rehabilitation of the back muscles and the spine. Notably, muscular force generated via eccentric contractions is significantly higher than concentric contractions (Nuzzo 2023). Thus, for a given 1RM, the eccentric contractions might be loaded suboptimal or potentially below the anabolic potential for the progressive resistive squat exercise program. Since eccentric and concentric loading can create differential loading patterns on bone, it is imperative to load the concentric and eccentric maximally for the maximal desired therapeutic outcome and design an effective progressive resistive squat exercise program. The importance of differentiating 1RM unique for concentric and eccentric contractions becomes more important with aging.

It is known that the eccentric strength of muscles is more greatly retained with age in comparison to concentric strength (Roig et al. 2010). The retention of eccentric contraction strength with aging comes from the contribution of titin and other associated structures that do not decline as greatly in capability as the myosin structures of muscles (Roig et al. 2010) (Power et al. 2016) (Miller et al. 2013; Hessel, Lindstedt, and Nishikawa 2017; Herzog 2018; Nuzzo et al. 2023). Furthermore, aging is associated with increased passive stiffness, connective tissue, and viscoelastic forces which can explain a greater retention of eccentric than concentric strength with aging (Singh et al. 2023). Importantly, a recent review showed that eccentric than concentric contraction biased exercises may have a greater utility for improving skeletal status in older adults (Singh et al. 2023). Thus, we posit that people with low bone mass may get greater benefit from eccentric‐biased exercises. Noticeably, eccentric muscle contractions are more energy efficient than concentric contractions for a given amount of muscle force and thus, are more beneficial than concentric contractions for the cardiovascular system (Hessel, Lindstedt, and Nishikawa 2017; Herzog 2018). It should be noted, however, that eccentric exercise can lead to significant muscle inflammation and muscle soreness (Margaritelis et al. 2021); however, those adverse effects disappear with continued training (Margaritelis et al. 2021). Thus, it is necessary to know the 1RM of both types of contractions to create scientifically informed and effective rehabilitation programs for strengthening bones of the vertebral column.

The maximum voluntary isometric squat strength has been utilized to predict the full squat 1RM in young adults, but the relationships and possible predictive capabilities between the maximum voluntary isometric squat strength and the unique concentric and eccentric maximum 1RM squat do not exist (Blazevich, Gill, and Newton 2002; Demura et al. 2010; Petrović et al. 2020). Knowledge of how the maximum voluntary isometric squat strength relates to the 1RM concentric and eccentric squat strength could help in the design of novel back strengthening rehabilitation programs creating specific anabolic stimuli for both the concentric and eccentric phases of the squat exercise. Such an approach can be especially important for musculoskeletal rehabilitation programs for older adults with chronic conditions of the skeletal system, such as osteoporosis (Haczyński, Jakimiuk, and Haczyƒski 2001).

Thus, the main purpose of this study was to determine if maximum voluntary isometric squat strength can predict 1RM concentric and eccentric squat strength in young and older adults. We hypothesized that maximum voluntary isometric squat strength predicts 1RM concentric and eccentric squat strength in young and older adults.

2. Methods

Data from two groups of participants: young (21–35 years, n = 15; men = 9, women = 6) and older adults (55–75 years, n = 14; men = 8, women = 6) are presented in our study. Our sample size is in line with a previous study with similar outcomes (Blazevich, Gill, and Newton 2002). Further, a prior power analysis was used to estimate the required sample size for the study. The statistical analysis was set for a linear regression: fixed model, single regression coefficient with effect size (f2) of 0.7, alpha error probability at 0.05, and power at 0.8. The calculated sample size was found to be 14 participants per group. We did not test anyone with a condition that limited their physical ability to fully perform our study's tests. Specific exclusion criteria included the following conditions: (1) uncontrolled diabetes; (2) uncontrolled hypertension; (3) metal screws/plates/rods in the body; (4) back surgery/myocardial infarction/congestive heart failure/cataract surgery/stroke within previous 6 months; (5) known prior vertebral fracture; (6) known fragility fracture within the last year; (7) tobacco use within the previous 10 years; (8) current use of medications that affect muscle/bone, such as hormone replacement therapy or corticosteroids; (9) back pain; and (10) uncontrolled hernia. The University of Alabama at Birmingham institutional review board approved this study.

2.1. Study Design

Our study used a cross‐sectional design to collect the experimental data. Our study consisted of two visits to the Physical Therapy Research Laboratory. The visits were at least a week apart from each other but no more than two weeks apart. The reason for the second visit was to allay any learning effect that may have occurred with the participants or to find their 1RM if it was not obtained during their first visit. We obtained the informed consent from our participants during their 1st visit. In addition, we performed anthropometric measurements during their 1st visit. For both the visits, we assessed the maximum voluntary isometric squat strength test first. Next, based on a simple randomization technique, we determined the order of testing of the 1RM concentric and eccentric squat strength test, unique to each participant. The 2nd visit consisted of squat strength testing with the maximum voluntary isometric squat strength testing performed first followed by the same randomized order of 1RM concentric and eccentric squat strength tests per the 1st visit of each participant. The highest values of the maximum voluntary isometric squat strength and 1RM concentric and eccentric squat strength were used for all the data analysis. A standard operating protocol was developed for conducting all the tests in this study. All the testers were trained in the standard operating protocol by a principal tester. Finally, all the tests were conducted following the standard operating protocol by the principal tester while student researchers supported the principal tester.

2.2. Anthropometric Measurements

At the first visit only, participants had their height taken in centimeters using a wall stadiometer (Novel Products Inc., Rockton, Illinois) and then their weight taken in kilograms using a digital physician's scale (Tanita Corporation of America, Arlington Heights, Illinois). We calculated Body Mass Index (BMI) using the formula, weight divided by height squared (kg/m2).

2.3. Warmup

To limit the risk of injury, individuals were asked to perform a warmup session before the testing. The warmup session consisted of participants using a stationary cycling bike or an elliptical machine for five minutes at a comfortable pace. In the last 30 s of the 5‐min warm up session, participants were asked to further slowdown and keep the warm‐up exercise to a minimum to prevent fatigue. Next, participants were provided a rest interval of 90‐s before any testing.

2.4. Goniometer

Wireless digital goniometers (Biometrics Corp., UK) were used to record and examine the angles of the knees before testing to find the appropriate depth for the squat position. Specifically, the knee goniometer crossed the knee joint of the dominant leg, with one end placed on the distal end of the femur and the other on or near the head of the fibula. To identify the dominant leg, participants were asked what leg they would kick a ball with. Data from the goniometers were relayed to the computer with the Biometric data analyst application that received, analyzed, and recorded the positioning and angle of the goniometer.

2.5. Maximum Voluntary Isometric Squat Strength Test

Individuals were asked to stand on a wooden platform placed beneath the Smith Machine (Body Solid, Forest Park, IL) and slowly descend to the required squat depth with a wireless goniometer attached to their knee. Next, the corresponding location on the Smith Machine was marked to be locked in for the barbell to be stationary during the isometric squat tests. The barbell was made stationary via ratchet straps that attached to the hooks on the wooden platform at both the ends of the barbell. The maximum voluntary isometric squat strength test via a Smith Machine was the first of the squat tests performed during both the trial visits for each individual. To record the isometric force exerted, a high‐performance strain gauge indicator (Omega, Norwalk, Connecticut) was utilized by attaching it to the barbell of the Smith machine and the stabilizing wooden plate below the barbell to record the isometric data in pounds. All the values were converted to kilograms for our data analysis.

Importantly, all our squat strength testing was performed on a Smith Machine at a 45‐degree flexion angle of the knee (45.91 ± 3.09). The partial squat (a 45‐degree flexion angle of the knee) position was chosen for all the squat testing trials instead of a full squat because the partial squat may be a safer option than the full deep squat while still maintaining the anabolic stimulating capabilities of the squatting exercise on the back muscles (Hartman et al. 2013). A partial squat than a full deep squat has also been identified to preferentially activate the erector spinae muscle group (Silva et al. 2017).

Participants were first familiarized with the test by trying to perform the test with submaximal force. Then, for testing, participants were asked to exert as much force as they could on the barbell and maintain it for five seconds. To limit the risk of injury and to help in the maintenance of form, participants were instructed and guided into a proper squat form. While this occurred, the strain gauge recorded the force exerted on the barbell and displayed the maximum amount of force exerted during each trial. Each participant was asked to perform five of these isometric tests during each visit with 90 s of rest interval between each trial. A trial was deemed a failure if the force exerted peaked and dipped repeatedly during the trials.

2.6. 1RM Concentric and Eccentric Squat Strength Tests

The 1RM concentric squat strength test consisted of finding the 1RM for the concentric squat, which involved the raising of the barbell. The barbell was first placed at the same position as during the maximum voluntary isometric squat strength test. The participants would raise the barbell in a controlled manner until they reached completion in the standing squat position. At the end, the barbell was locked in place and the weight was taken by the researchers. The barbell was returned to its original position between each trial by the research team to prevent the participant from performing the eccentric squat.

The 1RM eccentric squat strength test sought to find the 1RM maximum for the eccentric squat, that is, bringing the barbell down from their upright stand position, for each participant. This test involved bringing the barbell down from their standing squat position. The squat was complete when it reached the safety locks placed at a position where the knee angle was 45°. The Smith machine barbell was locked in this eccentric starting position through hooks on the barbell that could lock into the holes of the machine. The tester made sure the Smith machine's barbel was fully rested on the participant's shoulder before the participant was instructed to bring the barbell down to the resting/safety stops in a controlled manner. Next, the research team raised the barbell to prevent the participant from performing a concentric squat during these tests.

Both the tests preceded with the instructions and conditions written above until a failure to lift (concentric) or lower (eccentric) was reached or until all 8 trials for the visit had been performed. A trial was deemed a failure if an individual could not complete the squat fully or there was a loss of form, such as a shaky movement. After each trial, participants were asked to rate the difficulty of that trial using the Borg Rating of Perceived Exertion scale for safety.

A representative image of squat strength testing is provided in Figure 1.

FIGURE 1.

FIGURE 1

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Representative image showing the set‐up and starting position of maximum voluntary isometric squat strength (A), 1 repetition maximum eccentric squat strength (B), and 1 repetition maximum concentric squat strength (C) tests. The barbell was made stationary via ratchet straps that attached it to the hooks on the wooden platform at both the ends of the barbell, as shown in (A). A high‐performance strain gauge indicator (Omega, Norwalk, Connecticut) attached to the left ratchet straps connecting the barbell of the Smith machine and the stabilizing wooden plate below the barbell was used to record the isometric force as shown in (A). 1 repetition maximum eccentric squat strength test involved bringing the barbell down from the standing squat position as demonstrated in (B). 1 repetition maximum concentric squat strength test involved raising the barbell in a controlled manner until the standing squat position was reached from the same position as during the maximum voluntary isometric squat strength test as demonstrated in (C).

2.7. Statistical Analysis

Data were checked for normality using the skewness, kurtosis, and Shapiro–Wilk tests of normality. The descriptive statistics of both the young and older adults are presented as mean ± standard deviation (SD) (Table 1). The results for the recorded maximum squat strength for each of the three squat types were normalized to body weight. The analysis of the descriptive statistics was done using independent sample T‐tests. Linear regression was performed to analyze the relationship between the maximum voluntary isometric squat strength and the 1RM concentric and eccentric squat strength values in both age groups. The accepted alpha value was p < 0.05 in all statistical tests. Effect size for group differences (young vs. older) in maximum voluntary isometric squat strength, 1RM concentric squat and eccentric squat strength were assessed using Cohen's d, where the values of Cohen's d of 0.2, 0.5, and 0.8 represented small, medium, and large effect sizes (Cohen 1988).

TABLE 1.

Physical characteristics of study participants.

Variables Participants (n = 29) Two‐sided p
Younger (n = 15) Older (n = 14)
Age, y 23.67 ± 3.266 58.64 ± 2.925 < 0.001
Body weight (kg) 71.233 ± 13.424 83.287 ± 12.718 0.020
Height (M) 1.689 ± 0.098 1.737 ± 0.101 0.209
BMI (kg/m2) 24.862 ± 3.651 27.634 ± 3.816 0.056
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Abbreviation: BMI, Body Mass Index.

3. Results

The physical characteristics of the study participants are shown in Table 1. Older adults had greater body weight (p = 0.020) than young adults. There was a trend toward significance (p = 0.056) for a heavier BMI for older versus young adults.

Table 2 presents the values for both the absolute squat maximum and the normalized to body weight values for all the strength tests. Both the absolute and normalized 1RM concentric and eccentric squat strength measures were lower in older versus young adults (p = < 0.001–0.016, d = 0.96–1.49). The absolute and the normalized maximum voluntary isometric squat strength were not different between young versus older adults. Notably, the effect size ranged from mild (d = 0.39) to moderate (d = 0.65) with lower values of the absolute and the normalized maximum voluntary isometric squat strength for older versus. young adults.

TABLE 2.

Squat strength tests.

Variables Participants (n = 29) Two‐sided p Effect size
Younger (n = 15) Older (n = 14) Cohen's d
IsoMax (kg) 54.07 ± 27.54 45.4 ± 15.6 0.306 0.39
EccMax (kg) 175.8 ± 53.6 133.8 ± 30.04 0.016 0.96
ConMax (kg) 171.80 ± 54.8 119.8 ± 26.8 0.004 1.2
Normalized IsoMax 0.739 ± 0.291 0.565 ± 0.242 0.092 0.65
Normalized EccMax 2.494 ± 0.749 1.653 ± 0.477 0.001 1.33
Normalized ConMax 2.447 ± 0.794 1.485 ± 0.451 < 0.001 1.49
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Abbreviations: ConMax, 1 Repetition Maximum Eccentric Squat Strength; EccMax, 1 Repetition Maximum Eccentric Squat Strength; IsoMax, Maximum Voluntary Isometric Squat Strength.

Table 3 is broken down into three separate tables that present the predictor capabilities and relationship of the normalized maximum voluntary isometric squat strength in relation to the normalized 1RM concentric and eccentric squat strength. In the whole participant population, the normalized maximum voluntary isometric squat strength was found to be a significant predictor of 1) normalized 1RM eccentric squat strength (p = < 0.001, B = 1.015, ß = 0.605, r partial = 0.605) and 2) normalized 1RM concentric squat strength (p = 0.001, B = 0.810, ß = 0.618, r partial = 0.618). In young adults, no relationship existed between the normalized maximum voluntary isometric squat strength and the normalized 1RM eccentric or concentric squat strength (p = 0.058–0.085). In older adults, the normalized maximum voluntary isometric squat strength was a significant predictor of 1) normalized 1RM eccentric squat strength (p = 0.003, B = 0.844, ß = 0.727, r partial = 0.727) and 2) normalized 1RM concentric squat strength (p = 0.003, B = 0.709, ß = 0.737, r partial = 0.737).

TABLE 3.

Linear Regression analysis of normalized maximum voluntary isometric strength (IsoMax) versus normalized 1RM eccentric (EccMax) and concentric (ConMax) squat strength in the whole population (A), young adults (B), and older adults (C).

Dependent Predictor Unstandardized B constant Unstandardized B predictor Standardized β‐Coefficient r partial 95% confidence interval p
A
Normalized EccMax Normalized IsoMax 1.015 1.639 0.605 0.605 0.786–2.491 < 0.001
Normalized ConMax 0.810 1.790 0.618 0.618 0.891–2.689 < 0.001
B
Normalized EccMax Normalized IsoMax 1.622 1.180 0.459 0.459 −0.189 to 2.549 0.085
Normalized ConMax 1.439 1.364 0.500 0.500 −0.052 to 2.779 0.058
C
Normalized EccMax Normalized IsoMax 0.844 1.433 0.727 0.727 0.582–2.284 0.003
Normalized ConMax 0.708 1.376 0.737 0.737 0.583–2.169 0.003
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Note: β‐Coefficients display changes in SD in dependent variable per SD change in independent variable.

Figure 2 displays the novel regression equation: Normalized EccMax = 0.844 + 1.433 (Normalized IsoMax) predicting normalized 1RM eccentric squat strength based on normalized maximum voluntary isometric squat strength in older adults. Figure 3 displays the novel regression equation: Normalized ConMax = 0.708 + 1.376 (Normalized IsoMax) predicting normalized 1RM concentric squat strength based on normalized maximum voluntary isometric squat strength in older adults.

FIGURE 2.

FIGURE 2

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Linear regression of normalized Eccentric Squat Strength versus Normalized Maximum Voluntary Isometric Squat strength in older adults. EccMax: 1 repetition maximum eccentric squat strength; IsoMax = Maximum Voluntary Isometric Squat strength; Dotted lines represent 95% confidence interval range.

FIGURE 3.

FIGURE 3

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Linear regression of normalized 1 repetition maximum (RM) Concentric Squat Strength versus Normalized Maximum Voluntary Isometric Squat strength in older adults. ConMax: 1 repetition maximum eccentric squat strength; IsoMax = Maximum Voluntary Isometric Squat strength; Dotted lines represent 95% confidence interval range.

4. Discussion

To our knowledge, we are the first to report that the maximum voluntary isometric squat strength can predict 1RM concentric and eccentric squat strength in older adults (55–75 years). We also noted that the isometric maximum squat strength was not a predictor of the 1RM eccentric and concentric squat strength values in young adults (21–35 years). Our findings show that a safe technique for muscle strength assessment, such as isometric maximum squat strength, can be utilized in older populations to predict their 1RM of concentric and eccentric squat strength, and thus inform effective musculoskeletal rehabilitation programs for the back extensor muscle groups and the spine.

Multiple factors as discussed below can explain why the maximum isometric squat strength predicted 1RM concentric and eccentric squat strength in older adults only. Older adults do not only show aging‐associated deficits in muscle strength of the upper and lower extremities but also alterations in muscle fiber type and motor unit recruitment (Baum et al. 2009). For example, older versus young adults showed lower values of maximum isometric squat strength and1RM concentric and eccentric squat strength with effect sizes (Cohen's d) ranging from 0.65 to 1.5 in our study. It is well‐established that as we grow older, aging induces an increase in the proportion of type 1 fibers, while there is a decrease in the relative area of the type 2 fibers (Evans and Lexell 1995). Thus, we postulate that a combination of loss of muscle strength and fast‐twitch Type II muscle fibers may explain the well‐known observation of compensatory increase in motor unit recruitment in middle‐aged and older adults (Ling et al. 2009). In addition, there is some evidence that motor unit recruitment is consistent to a greater degree in older than young adults (Kirk et al. 2021). Thus, we surmise that low muscle strength, an increased role of Type 1 muscle fibers with all the different types of squats (isometric, concentric, and eccentric) in our study and a consistently high and similar level of motor unit recruitment across different types of squats in older adults can explain why maximum isometric squat strength, 1RM concentric and eccentric squat strength were highly related with each other. It will be interesting to examine if similar findings would hold true for highly physically active older adults or if the findings would hold true in older adults after a resistance training program.

In young adults, preferential recruitment of Type I versus II muscle fibers to produce maximal strength and the accompanying variable level of motor unit recruitment with different types of squats may explain our non‐significant finding of any relationship between maximum isometric squat strength and 1RM concentric and eccentric squat strength (Kay et al. 2000; Kirk et al. 2021). Moreover, non‐concordant relationships between maximum isometric squat strength and 1RM squat strength have been reported before in young athletes (Wagner et al. 2022). Interestingly, relationships between maximum isometric squat strength and 1RM concentric and eccentric squat strength are unknown in young adults with pathological conditions affecting the musculature of the back, such as chronic low back pain and could be an exciting area of investigation.

Older adults have been found to maintain their eccentric strength with aging, in contrast to concentric and isometric strength that is found to significantly decrease with age (Power et al. 2016; Roig et al. 2010). This conservation has led to a unique difference in comparing eccentric and isometric muscle strengths between age groups, where older populations demonstrate much higher ratios of eccentric strength to isometric strength than young adults (Power et al. 2015, 2016). Markedly, young adults have lower differences between their eccentric, isometric, and even concentric squat maximum strength (Power et al. 2016). In our study, the 1RM eccentric squat maximum/maximum isometric squat strength and 1RM concentric squat maximum/maximum isometric squat strength ratios for young adults were 3.3, whereas they were < 3 in older adults. It is unknown if the difference in ratios of the aforementioned squat types could contribute to unique predictive capabilities of maximum isometric squat strength in older adults.

4.1. Limitations

Although the sample size for both young and older groups met the necessary power requirements, the sample size was still relatively small. Because of the low sample size, we were unable to fully analyze whether our prediction equations were affected by sex for each group. Examining whether sex could affect our results is important because previous literature has also shown that some of the age‐based degradation in muscular contractions is significantly affected by sex, further highlighting the importance of sex and age being analyzed together (Miller et al. 2013). Future studies should examine whether sex can affect the predictive ability of maximum isometric squat for 1RM concentric and eccentric squat strength in young and older adults. The use of the Borg's exertion scale is well supported but also serves as a limitation as it requires the participant's opinion (William 2017). Finally, we did not collect data on physical activity to see if that could have affected our results.

5. Implications for Physiotherapy Practice

Overall, our novel findings show that safe techniques for muscle strength assessment, such as maximum voluntary isometric squat strength, can be utilized in older populations to predict their 1RM of concentric and eccentric squat strength. Our novel equations provide the information necessary for designing effective rehabilitation regimes for strengthening the muscles and bone of the back in older adults.

Ethics Statement

This study was approved by the local Institutional Review Board.

Consent

Informed consent form was obtained from all the participants.

Conflicts of Interest

The authors declare no conflicts of interest.

Permission to Reproduce Material From Other Sources

The authors have nothing to report.

Acknowledgments

This study would not have been completed without the support of our participants. We also thank Dr. Jeffrey Morris, Department of Biology, University of Alabama at Birmingham, who provided valuable feedback related to this study.

Funding: The authors received no specific funding for this work.

Data Availability Statement

Study data are available on request to the corresponding author.

References

  1. Baum, K. , Hildebrandt U., Edel K., et al. 2009. “Comparison of Skeletal Muscle Strength Between Cardiac Patients and Age‐Matched Healthy Controls.” International Journal of Medical Sciences 6, no. 4: 184–191. 10.7150/ijms.6.184. [DOI] [PMC free article] [PubMed] [Google Scholar]
  2. Blazevich, A. J. , Gill N., and Newton R. U.. 2002. “Reliability and Validity of Two Isometric Squat Tests.” Journal of Strength & Conditioning Research 16, no. 2: 298–304. . [DOI] [PubMed] [Google Scholar]
  3. Braith, R. , Graves J. E., Leggett S. H., and Pollock M. L.. 1993. “Effect of Training on the Relationship Between Maximal and Submaximal Strength.” Medicine & Science in Sports & Exercise 25, no. 1: 132–138. 10.1249/00005768-199301000-00018. [DOI] [PubMed] [Google Scholar]
  4. Cohen, J. 1988. Statistical Power Analysis for the Behavioral Sciences. 2nd ed. Hillsdale, NJ: Lawrence Erlbaum Associates, Publishers. 10.4324/9780203771587. [DOI] [Google Scholar]
  5. Cormie, P. , Mccaulley G. O., Triplett N. T., and Mcbride J. M.. 2007. “Optimal Loading for Maximal Power Output During Lower‐Body Resistance Exercises.” Medicine & Science in Sports & Exercise 39, no. 2: 340–349. 10.1249/01.mss.0000246993.71599.bf. [DOI] [PubMed] [Google Scholar]
  6. Da Silva, J. J. , Schoenfeld B. J., Marchetti P. N., Pecoraro S. L., Greve J. M., and Marchetti P. H.. 2017. “Muscle Activation Differs Between Partial and Full Back Squat Exercise With External Load Equated.” Journal of Strength and Condition Research 31, no. 6: 1688–1693. 10.1519/jsc.0000000000001713. [DOI] [PubMed] [Google Scholar]
  7. Demura, S. , Miyaguchi K., Shin S., and Uchida Y.. 2010. “Effectiveness of the 1RM Estimation Method Based on Isometric Squat Using a Back‐Dynamometer.” Journal of Strength & Conditioning Research 24, no. 10: 2742–2748. 10.1519/JSC.0b013e3181e27386. [DOI] [PubMed] [Google Scholar]
  8. Drake, D. , Kennedy R., and Wallce E.. 2018. “Familiarization, Validity, and Smallest Detectable Difference of the Isometric Squat Test in Evaluating Maximal Strength.” Journal of Sports Sciences 36, no. 18: 2087–2095. 10.1080/02640414.2018.1436857. [DOI] [PubMed] [Google Scholar]
  9. Evans, W. , and Lexell J.. 1995. “Human Aging, Muscle Mass, and Fiber Type Composition.” Journals of Gerontology Series A Biological Sciences and Medical Sciences 50, no. A: 11–16. 10.1093/gerona/50a.special_issue.11. [DOI] [PubMed] [Google Scholar]
  10. Grgic, J. , Lazinica B., Schoenfeld B. J., and Pedisic Z.. 2020. “Test–Retest Reliability of the One‐Repetition Maximum (1RM) Strength Assessment: A Systematic Review.” Sports Medicine Open 6, no. 1: 31. 10.1186/s40798-020-00260-z. [DOI] [PMC free article] [PubMed] [Google Scholar]
  11. Haczyński, J. , Jakimiuk A. J., and Haczyƒski J.. 2001. “Vertebral Fractures: A Hidden Problem of Osteoporosis.” Medical Science Monitor 7, no. 5: 1108–1117. [PubMed] [Google Scholar]
  12. Hartmann, H. , Wirth K., and Klusemann M.. 2013. “Analysis of the Load on the Knee Joint and Vertebral Column With Changes in Squatting Depth and Weight Load.” Sports Medicine 43, no. 10: 993–1008. 10.1007/s40279-013-0073-6. [DOI] [PubMed] [Google Scholar]
  13. Herzog, W. 2018. “The Multiple Roles of Titin in Muscle Contraction and Force Production.” Biophysical Reviews 10, no. 4: 1187–1199. 10.1007/s12551-017-0395-y. [DOI] [PMC free article] [PubMed] [Google Scholar]
  14. Hessel, A. L. , Lindstedt S. L., and Nishikawa K. C.. 2017. “Physiological Mechanisms of Eccentric Contraction and Its Applications: A Role for the Giant Titin Protein.” Frontiers in Physiology 8, no. 1: 70. 10.3389/fphys.2017.00070. [DOI] [PMC free article] [PubMed] [Google Scholar]
  15. Kay, D. , St Clair Gibson A., Mitchell M., Lambert M., and Noakes T.. 2000. “Different Neuromuscular Recruitment Patterns During Eccentric, Concentric and Isometric Contractions.” Journal of Electromyography and Kinesiology 10, no. 6: 425–431. 10.1016/S1050-6411(00)00031-6. [DOI] [PubMed] [Google Scholar]
  16. Kirk, E. , Christie A. D., Knight C. A., and Rice C. L.. 2021. “Motor Unit Firing Rates During Constant Isometric Contraction: Establishing and Comparing an Age‐Related Pattern Among Muscles.” Journal of Applied Physiology 130, no. 6: 1903–1914. 10.1152/japplphysiol.01047.2020. [DOI] [PubMed] [Google Scholar]
  17. Ling, S. , Conwit R. A., Ferrucci L., and Metter E. J.. 2009. “Age‐Associated Changes in Motor Unit Physiology: Observations From the Baltimore Longitudinal Study of Aging.” Archives of Physical Medicine and Rehabilitation 90, no. 7: 1237–1240. 10.1016/j.apmr.2008.09.565. [DOI] [PMC free article] [PubMed] [Google Scholar]
  18. Lum, D. , Haff G. G., and Barbosa T. M.. 2020. “The Relationship Between Isometric Force‐Time Characteristics and Dynamic Performance: A Systematic Review.” Sports 8, no. 5: 63. 10.3390/sports8050063. [DOI] [PMC free article] [PubMed] [Google Scholar]
  19. Margaritelis, N. V. , Theodorou A. A., Chatzinikolaou P. N., Kyparos A., Nikolaidis M. G., and Paschalis V.. 2021. “Eccentric Exercise Per Se Does Not Affect Muscle Damage Biomarkers: Early and Late Phase Adaptations.” European Journal of Applied Physiology 121, no. 2: 549–559. 10.1007/s00421-020-04528-w. [DOI] [PubMed] [Google Scholar]
  20. Mccurdy, K. , Langford G. A., Cline A. L., Doscher M., and Hoff R.. 2004. “The Reliability of 1‐ and 3RM Tests of Unilateral Strength in Trained and Untrained Men and Women.” Journal of Sports Science and Medicine 3, no. 3: 190–196. [PMC free article] [PubMed] [Google Scholar]
  21. Miller, M. , Bedrin N. G., Callahan D. M., et al. 2013. “Age‐Related Slowing of Myosin Actin Cross‐Bridge Kinetics is Sex Specific and Predicts Decrements in Whole Skeletal Muscle Performance in Humans.” Journal of Applied Physiology 115, no. 7: 1004–1014. 10.1152/japplphysiol.00563.2013. [DOI] [PMC free article] [PubMed] [Google Scholar]
  22. Myer, G. D. , Kushner A. M., Brent J. L., et al. 2014. “The Back Squat: A Proposed Assessment of Functional Deficits and Technical Factors That Limit Performance.” Strength and Conditioning Journal 36, no. 6: 4–27. 10.1519/SSC.0000000000000103. [DOI] [PMC free article] [PubMed] [Google Scholar]
  23. Nuzzo, J. L. , Pinto M. D., Nosaka K., and Steele J.. 2023. “The Eccentric:Concentric Strength Ratio of Human Skeletal Muscle in Vivo: Meta‐Analysis of the Influences of Sex, Age, Joint Action, and Velocity.” Sports Medicine 53, no. 6: 1125–1136. 10.1007/s40279-023-01851-y. [DOI] [PMC free article] [PubMed] [Google Scholar]
  24. Parai, M. , Shenoy P., Velayutham S., Seng C., and Yee C. F.. 2016. “Isometric Muscle Strength as a Predictor of One Repetition Maximum in Healthy Adult Females: A Crossover Trial.” Clinical and Translational Orthopedics 1, no. 2: 0. 10.4103/2468-5674.183005. [DOI] [Google Scholar]
  25. Petrović, B. , Kukrić A., Dobraš R., and Zlojutro N.. 2020. “Maximum Isometric Muscle Strength as a Predictor of One Repetition Maximum in the Squat Test.” Sportlogia 16, no. 1: 161–172. 10.5550/sgia.201601.en.pkdz. [DOI] [Google Scholar]
  26. Power, G. , Flaaten N., Dalton B. H., and Herzog W.. 2016. “Age‐Related Maintenance of Eccentric Strength: A Study of Temperature Dependence.” Age 38, no. 2: 43. 10.1007/s11357-016-9905-2. [DOI] [PMC free article] [PubMed] [Google Scholar]
  27. Power, G. , Makrakos D. P., Stevens D. E., Rice C. L., and Vandervoort A. A.. 2015. “Velocity Dependence of Eccentric Strength in Young and Old Men: The Need for Speed.” Applied Physiology Nutrition and Metabolism 40, no. 7: 703–710. 10.1139/apnm-2014-0543. [DOI] [PubMed] [Google Scholar]
  28. Roig, M. , MacIntyre D. L., Eng J. J., Narici M. V., Maganaris C. N., and Reid W. D.. 2010. “Preservation of Eccentric Strength in Older Adults: Evidence, Mechanisms and Implications for Training and Rehabilitation.” Experimental Gerontology 45, no. 6: 400–409. 10.1016/j.exger.2010.03.008. [DOI] [PMC free article] [PubMed] [Google Scholar]
  29. Salari, N. , Ghasemi H., Mohammadi L., et al. 2021. “The Global Prevalence of Osteoporosis in the World: A Comprehensive Systematic Review and Meta‐Analysis.” Journal of Orthopedic Surgery and Research 16, no. 1: 669. 10.1186/s13018-021-02772-0. [DOI] [PMC free article] [PubMed] [Google Scholar]
  30. Schoenfeld, B. J. , Grgic J., Van Every D. W., and Plotkin D. L.. 2021. “Loading Recommendations for Muscle Strength, Hypertrophy, and Local Endurance: A Re‐Examination of the Repetition Continuum.” Sports 9, no. 2: 32. 10.3390/sports9020032. [DOI] [PMC free article] [PubMed] [Google Scholar]
  31. Shaw, C. , McCully K., and Posner J.. 1995. “Injuries During the One Repetition Maximum Assessment in the Elderly.” Journal of Cardiopulmonary Rehabilitation 15, no. 4: 283–287. 10.1097/00008483-199507000-00005. [DOI] [PubMed] [Google Scholar]
  32. Shirado, O. , Ito T., Kaneda K., and Strax T. E.. 1995. “Concentric and Eccentric Strength of Trunk Muscles: Influence of Test Postures on Strength and Characteristics of Patients With Chronic Low‐Back Pain.” Archives of Physical Medicine and Rehabilitation 76, no. 7: 604–611. 10.1016/s0003-9993(95)80628-8. [DOI] [PubMed] [Google Scholar]
  33. Singh, H. , Moore B. A., Rathore R., et al. 2023. “Skeletal Effects of Eccentric Strengthening Exercise: A Scoping Review.” BMC Musculoskeletal Disorders 24, no. 1: 611. 10.1186/s12891-023-06739-6. [DOI] [PMC free article] [PubMed] [Google Scholar]
  34. Wagner, C. M. , Warneke K., Bächer C., et al. 2022. “Despite Good Correlations, There is No Exact Coincidence Between Isometric and Dynamic Strength Measurements in Elite Youth Soccer Players.” Sports 10, no. 11: 175. 10.3390/sports10110175. [DOI] [PMC free article] [PubMed] [Google Scholar]
  35. Warneke, K. , Wagner C. M., Keiner M., et al. 2023. “Maximal Strength Measurement: A Critical Evaluation of Common Methods ‐ a Narrative Review.” Frontiers in Sports and Active Living 17, no. 5: 1105201. 10.3389/fspor.2023.1105201. [DOI] [PMC free article] [PubMed] [Google Scholar]
  36. Wilk, M. , Petr M., Krzysztofik M., Zajac A., and Stastny P.. 2018. “Endocrine Response to High Intensity Barbell Squats Performed With Constant Movement Tempo and Variable Training Volume.” Neuroendocrinology Letters 39, no. 4: 342–348. [PubMed] [Google Scholar]
  37. Williams, N. 2017. “The Borg Rating of Perceived Exertion (RPE) Scale.” Occupational Medicine 67, no. 5: 404–405. 10.1093/occmed/kqx063. [DOI] [Google Scholar]

Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Data Availability Statement

Study data are available on request to the corresponding author.

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