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EFFECTS OF CONTROLLED WHOLE-BODY VIBRATION TRAINING ON FUNCTIONAL PERFORMANCE AMONG HEALTHY OLDER ADULTS: A 6-WEEK PILOT STUDY

 

F. Saucedo1, E.A. Chavez2, H.R. Vanderhoof2, J.D. Eggleston2,3

 

1. Department of Kinesiology, Penn State Altoona, Altoona, PA, USA; 2. Interdisciplinary Health Sciences Doctoral Program, The University of Texas at El Paso, El Paso, TX, USA; 3. Department of Kinesiology, The University of Texas at El Paso, El Paso, TX, USA

Corresponding Author: Fabricio Saucedo, PhD, Department of Kinesiology, Penn State Altoona, 300 Ivyside Park, Rm. 203, Altoona, Pennsylvania 16601, USA, Tel: +1-814-949-5307, E-mail: fns5045@psu.edu

J Aging Res & Lifestyle 2021;10:39-44
Published online June 7, 2021, http://dx.doi.org/10.14283/jarlife.2021.7

 

Abstract

Background: Falling is the second leading cause of injury-related death worldwide and is a leading cause of injury among older adults. Whole-body vibration has been used to improve fall risk factors in older adults. No study has assessed if vibration benefits can be retained over time. Objectives: The aims of this study were to examine if six-weeks of whole-body vibration could improve fall risk factors and to assess if benefits associated with the training program could be sustained two months following the final training session. Design and Setting: Repeated measures randomized controlled design. Participants: Twenty-four independent living older adults were recruited and were randomly assigned to the WBV or control group. Intervention: Participants performed three sessions of whole-body vibration training per week with a vibration frequency of 20Hz or with only an audio recording of the vibration noise. An assessment of fall risk factors was performed prior to, immediately following, and two-months after the completion of the training program. Main Outcome Measures: Fall risk factors including functional capacity, mobility, strength, and walking speed were assessed pre-training, post-training, and two-months post-training. Results: Seventeen participants completed the study. No improvements (p<0.05) between groups were found in the measures of physical performance. Conclusions: Findings revealed that six weeks of whole-body vibration is not effective in improving fall risk factors or producing benefits post-training.

Key words: Vibration exercise, fall prevention, muscle strength, retention, functional mobility.

 

Introduction

Falling is the second leading cause of injury-related death worldwide (1) and is a leading cause of injury among older adults. More than one-third of older adults in the United States will fall in a given year (2) and considering the increased prevalence of falls among this age group (i.e. 60 years and older), this presents a significant global healthcare and economic issue (3). Reports have shown that up to 29 million community dwelling older adults experience falls each year, resulting in 7 million injuries requiring medical treatment (4).
Age-related changes in physical performance expose older adults to increased falls risk and high fall-related morbidity (5) and thus, the main focus of interventions should focus on improving performance in areas related to falls. Traditional approaches such as aerobic or resistance training have attempted to improve physical performance to mitigate risk factors associated with increased falls, such as muscle weakness, decreased mobility sensory loss, and deficits in balance (6). However, despite significant efforts, limitations such as physical ability (7) have prevented access and have affected long-term adherence to traditional exercise programs.
Recently, whole-body vibration (WBV) has been utilized to train older adults to improve physical performance (8). Compared to traditional exercise programs, WBV is less strenuous, can be portable and cost-effective, and requires minimal exercise experience (8). Participants stand on the vibration platform and experience low frequency mechanical stimulation, which stimulates the muscle spindles (9). This activates alpha-motor neurons in the central nervous system which elicits tonic muscle contractions in the lower extremities (9). The transmission of vibrations and oscillations to the human body can lead to physiological changes on numerous levels (10). Studies have demonstrated that vibration can nurture coordination and improve muscle strength, which can be an effective method in improving postural control in older adults (11). This has been demonstrated in studies examining six-week training periods, which have demonstrated neuromuscular adaptations and increases in neural activation (12), which in turn might have aid physical performance or lead to acute benefits.
Although several studies have examined the effects of WBV in older adults, only four other studies have assessed if WBV benefits can be retained over time (13–16). These studies assessed performance after a washout period of three weeks, three months, and six months, respectively, and found that participants were not able to sustain WBV training benefits. Therefore, it is not certain if WBV exercise can produce health and performance benefits following the cessation of a training program. Thus, the purposes of this study were to examine if a six-week course of WBV training could improve fall risk factors and to examine if benefits of WBV could be retained over a two-month period after completing the program. It was hypothesized that six weeks of WBV would improve fall risk factors compared to a control (CON) group. Additionally, it was hypothesized that benefits associated with WBV would be sustained over the two-month period following the completion of the WBV program.

 

Methods

Participants

Twenty-four older adults between the ages of 60-85 with physician clearance, no history of neurological, cognitive, musculoskeletal, cardiovascular, or known gait impairments were recruited for the study (Figure 1). Participants were recruited via advertisements on social media and flyers throughout the Greater El Paso, Texas Region and through our contacts with different institutes and hospitals in the city of El Paso. From the initial 24 recruits, only seventeen participants (13 female and 4 male) ages (70.4 ± 6.2 years) completed the study (Table 1); seven participants did not complete the study due to research restrictions from the COVID-19 global pandemic. Participants were randomly assigned into one of two groups (WBV n=9 or CON n=8) using a random number generator and were briefed on all procedures. Participants were not aware of their assignment into the CON or WBV group and this information was withheld for the duration of the study. Participants provided written informed consent approved by the University’s Institutional Review Board. This was a pilot study utilizing a randomized controlled design and was performed in accordance with the ethical standards as described by the 1964 Declaration of Helsinki.

Figure 1
Study flowchart outlining participant recruitment, randomization, and course of study

Table 1
Group demographic parameters for participants in the whole-body vibration and control group

Values are n, mean ± standard deviation, or as otherwise indicated

Assessment of functional mobility

Functional mobility was evaluated using the timed-up-and-go test (TUG). Participants rose from an armed chair with no use of the arms, walked forward three meters, crossed a marked line on the floor and returned to the original seated position. The test began when the investigator said “go” and ended when the participant returned to the seated position. Participants were instructed to complete the task quickly and safely. The total time taken to complete the task at maximal speed was used for analysis.

Functional capacity was assessed using the two-minute walk test (2MWT). Participants were instructed to walk for two minutes between two cones set 30.48 meters apart. Participants were permitted to rest during the two-minute test but were made aware that the timer would continue to run until time expired. Total distance traveled during the two-minutes was used as a measure of functional capacity.

Assessment of walking speed

Participants performed three walking trials of self-selected normal gait along a 10-meter straight walkway (10MWT). Time to complete each trial in seconds was recorded to the hundredth second. The mean of the of the three trials was used for analysis.

Assessment of muscle strength

Maximum isometric torque of the quadriceps and hamstrings was assessed for all participants. Participants completed a standardized warm-up and test protocol on a motor-driven dynamometer (System 3, Biodex Medical Systems, Inc., Shirley, NY). The knee extension/flexion isometric strength assessment was performed bilaterally, in a seated position on a posterior-inclined (15º) chair. The proximal portion of the leg, pelvis, and shoulders were stabilized with safety belts. The rotational axis of the dynamometer was aligned with the mediolateral knee-joint axis and connected to the distal end of the tibia using an adjustable rigid lever arm. The three-dimensional positions of the rotational axis, the position of the chair, and the length of the lever arm were recorded and were identical for the strength assessment during the other testing sessions (e.g., post-training and two-month follow-up). Each participant performed three repetitions, each lasting seven seconds for both flexion and extension on the dominant and non-dominant leg. Leg dominance was identified by asking the participant which leg would be used to kick a ball. One-minute resting periods were administered between repetitions. The average maximum torque normalized to body mass (Newton-meter/kilogram (Nm/kg)) from the three trials was used for analysis.

Training Intervention

During each training, participants in the WBV group completed one set of vibration training. The training was intermittent with one-minute vibration sessions followed by a one-minute rest, for a total of 10 minutes (Figure 2). To avoid adverse effects or discomfort while on the vibration platform, knee flexion was maintained at 20º (17). To minimize the shoe-dampening effect, participants stood on the platform barefoot. A side-alternating vibration platform (Galileo Med-L, Germany) was used and is depicted in Figure 2. The platform rotated about an anteroposterior axis, so positioning the feet farther from the axis of rotation would result in larger-amplitude vibration. The vibrator provided stimulation at fixed frequency of 20 Hz with the vibration amplitude set to 1.3 mm, a setting designed to stimulate the stretch reflex and promote muscle function (Galileo Med-L, German). This vibration frequency was selected to maximize comfort and retention in the protocol and to reduce the risk of excess stimulation or resonating of the physiological systems (18). The assessments for physical performance described previously were performed in the morning hours prior to training (pre), immediately following the completing of the six-week WBV program (post), and two months after the completion of the protocol for retention (rtn). All sessions were performed in the laboratory at The University of Texas at El Paso all assessors were not blinded to participant group allocation.

Schematics of (a) the whole-body vibration timeline and protocol breakdown and (b) participant set-up on the side-alternation vibration platform. Vibrations were delivered intermittently at a frequency of 20 Hz and a vibration amplitude of 1.3mm

 

The CON group completed an identical program with no vibration. An audio recording of the vibrator motor was played during the session to mimic the sound of the WBV protocol (19).
Training sessions occurred three times per week, for six weeks. At least 24 hours were observed between consecutive training sessions. Successful completion of the programs occurred when each participant completed 18 sessions. Training sessions were supervised and conducted individually to monitor participant status and note any adverse mild effects potentially associated with training (itching, edema of the legs, soreness) (20). Participants were instructed to hold a stability bar attached to the vibration platform to minimize any fall risk.

Statistical analyses

An a priori sample estimate of 32 participants was calculated in G-Power 3.1 with a critical alpha-level set at 0.05, a large effect size (d= 1.03), and power of 0.80. Analyses were performed using SPSS software version 24 (IBM, Armonk, New York). A Chi-Square Test was conducted to assess between group differences in baseline characteristics and Fisher’s Exact Test was used to denote significance. Repeated measures analysis of variance (ANOVA) was used to identify the effect of WBV training on muscle strength, and performance on the TUG, 2MWT, and 10MWT. The within subject factor was the time instances (pre vs. post vs. rtn) while group (WBV vs. CON) served as the between subject factor. An alpha level of p <0.05 was used to determine statistical significance.

Results

Baseline characteristics are presented in Table 1. The Chi-Square Test revealed no differences in gender
between groups and no differences were identified between groups in age (yrs.), height (m), or mass (kg). No significant time by group 2-way interaction was detected for any of the variables (Table 2), however, isometric extension of the left leg approached significance (p =0.090) (Figure. 4b). The ANOVA revealed a significant main effect of time for the 10MWT (p =0.033) (Figure. 3a) and the 2MWT (p =0.013) (Figure. 3b), but not for the TUG test (Figure. 3c) or the right and left measures of leg strength (Figure. 4a-b). Mean and standard error values are displayed in Figures 3 and 4.

Table 2
Performance outcomes for the control and whole-body vibration group for all testing periods

TUG: Timed Up and Go test; 2MWT: Two-minute walking test; 10MWT: 10-meter walking test. p-value reflects between-group differences

Figure 3
Group means and standard error bars for (a)10MWT, (b) 2MWT, and (c) TUG Test for the pre-test (Pre), post-test (Post), and two-month retention (Rtn). Asterisk (*) indicates within group differences p<0.05 for the duration of the study

Figure 4
Group means and standard error bars for the (a-b) right and left max extensor torque and (c-d) right and left max flexor torque for the pre-test (Pre), post-test (Post), and two-month retention (Rtn)

 

Discussion

The aims of this study were to examine if six-weeks of WBV training could improve fall risk factors in older adults and to examine whether WBV benefits could be retained at least two months after completion of the WBV program. It was hypothesized that participants in the WBV group would improve in all fall risk factors. Additionally, it was hypothesized that all performance benefits associated with WBV would be retained in participants after two months. Based on the study findings, the hypotheses were not supported.
Other studies have also shown that WBV is no more effective than placebo conditions or traditional methods of intervention (21, 22). The findings from these studies as well as our study contrast those reported previously (23, 24). The study by Kawanabe and colleagues (2007) found that incorporating WBV training into a conventional regimen consisting of lower extremity strength exercises significantly improved walking speed in the 10MWT compared to the exercise-only group. Simão et al., (2012) determined that WBV signifcanlty improved distance walked during the 6MWT (similar to our 2MWT), and walking speed in the 10MWT. However, much like the study by Kawanabe et al., (2007), the participants in the study underwent a combination of WBV and squat therapy (24). Several other studies have reported performance improvements associated with WBV, but these too have combined exercise with a WBV regimen (19, 25).

Few studies conducted previously have implemented protocols similar to our study. One study reported significant between group differences with participants in the WBV group showing greater increases in muscle strength and muscle hypertrophy compared to the control group (26). Another study reported significant improvements in participants who underwent 8-weeks of WBV. Participants experienced improvements in isometric knee extensor and flexor strength (8). This study did not include a control group, as our study, limiting their ability directly link performance benefits to the intervention.
Our study did not provide any evidence indicating any performance improvements linked to WBV. One possible reason for this outcome may relate to the duration of the study intervention. Other studies have commonly implemented WBV training periods lasting between three and eight months (25, 27). While the six-week period that we chose may be sufficient to yield neuromuscular adaptations or increase neural activation (12), which in turn might have aided physical performance or lead to acute benefits, it may be possible that six weeks does not suffice to obtain benefits from WBV. Other studies have implemented six-week WBV interventions in older adults and have reported improved balance and mobility/walking scores (19, 28). With the exception of the findings reported by Sitja-Rabert et al., (22), which found no improvements in physical performance in older adults after a six-week vibration intervention, studies implementing six-week interventions have shown improvements in fall risk factors and therefore other explanations for the findings in our study must be considered.
We acknowledge several limitations in this study. One possible limitation is that the training intensity and frequency were not adequate to elicit physiological changes linked to the improvements in the fall risk factors. The vibration frequency selected for the current study was 20 Hz and it was delivered intermittently for 60-seconds for a total of five-minutes, three times weekly. Vibration frequencies ranging from 12.5 to 20 Hz have typically been classified as low-intensity, while frequencies from 30-50 Hz have been classified as high-intensity (29). In theory, higher vibration frequencies elicit greater responses from the proprioceptors of the lower-extremities, however, many studies have shown that WBV interventions utilizing 20 Hz still result in improved performance outcomes (i.e. lower falls risk) (8). Another limitation that might have resulted in lack of significant findings in the present study is potentially attributed to the small sample size. Based on the a priori sample size estimation, a total of 32 participants was required to achieve sufficient statistical power. A posteriori power-analysis revealed that with the 17 total participants that were recruited, the present study only yielded a statistical power of 0.22 at the 0.05 alpha level, thereby increasing the likelihood of type 2 error. Considering the smaller sample size composed of generally healthy and high-functioning participants, a ceiling effect could have resulted. The COVID-19 global pandemic impacted the study sample size, but future studies will aim to increase the study sample size to increase study power. One final limitation may be linked to the methodology that was utilized in the study. Isokinetic dynamometry was used to assess leg strength, specifically knee flexion and extension torque and no significant findings were found. While WBV can be effective in stimulating proprioception of the lower extremity, the vibratory stimulation is mainly targeted distally at the ankle joint because this is where the majority of the signal is dampened. Therefore, it would be more appropriate for future studies to examine ankle plantarflexion and dorsiflexion. This may also be beneficial as the plantarflexion and dorsiflexion play a vital role in the ankle mechanism for postural control.
The overall conclusion from this study was that six-weeks of WBV was not effective in improving physical performance on fall risk assessments among healthy older adults. While the findings from this study did not reveal statistically significant findings, there is one key strength which should be emphasized. This study represents the only one of a few studies to have looked at possible retention of benefits in older adults. Although not significant, this study could potentially be utilized in the scientific community to modify and design future protocols to examine the effects of WBV on risk factors associated with falls and retention among older adults. Future studies are required to identify the full benefits of WBV on improving performance fall risk factors in older adults.

 

Conflict of interest: None declared.

Acknowledgments: The authors thank Bianca Tovar, Alyssa Olivas, Pearl Quintero, and Christian Sanchez for their assistance

Funding sources: This study was funded The University of Texas at El Paso Dodson Research Grant, the Texas American College of Sports Medicine Student Research Development Award, and a generous contribution from the Virtual Reality and Motor Control Research Laboratory directed by Dr. Jason Boyle.

 

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DEFINING SARCOPENIA USING MUSCLE QUALITY INDEX

 

C.-D. Lee, E. Dierickx

 

School of Nutrition and Health Promotion, Arizona State University, Phoenix, AZ;

Corresponding Author: Dr. Chong Lee, Arizona State University, School of Nutrition and Health Promotion, 500 North 3rd street, Phoenix, AZ 85004, Phone: 602-827-2282, Fax: 602-496-1873, Email: chong.lee@asu.edu

J Aging Res Clin Practice 2018;7:45-59
Published online March 29, 2018, http://dx.doi.org/10.14283/jarcp.2018.11

 

Abstract

Objectives: Although low muscle quality is a strong predictor of sarcopenia, defining sarcopenia using muscle quality remains unknown.  This study investigated the cut-points to define sarcopenia using muscle quality index (MQI) in the young reference population. Methods: Fifty healthy young (20 to 29 years) and forty elderly adults (60 to 79 years) were recruited in this study.  Dual-energy X-ray absorptiometry was used to assess appendicular skeletal muscle mass.  Hand grip and leg dynamometers were used to measure muscle strengths in the arm and leg.  Muscle quality in the arm (MQIArm, kg/kg) and leg (MQILeg, Nm/kg) were computed as muscle strength per lean mass in the arm and leg, respectively.  Total muscle quality (MQITotal) was computed as the combination of MQIArm and MQILeg, while standardized muscle quality (MQIStd) was computed as the combination of z-scores in MQIArm and MQILeg.  Sarcopenia was defined as ≤2 SD below from the mean values in the young reference group.  Results: The cut-points for defining sarcopenia using MQIArm, MQILeg, MQITotal, and MQIStd in men were ≤8.37, ≤12.07, 22.06, and <-3.35, and in women were ≤10.09, ≤13.97, 28.22, and <-2.25, respectively.  In the elderly adults, the frequencies of sarcopenia using MQIArm, MQILeg, MQITotal, and MQIStd were 15%, 27.5%, 32.5%, and 35%, respectively. Conclusion: This study establishes new values for defining sarcopenia using MQIs.  The proposed new MQI cut-points may be a role in detecting sarcopenia across individual and population level.

Key words: sarcopenia, muscle quality index, muscle mass, muscle strength.

 

Introduction

Age-related skeletal muscle loss (sarcopenia) is a significant risk factor for falls (1), disability (2), and mortality (3) in the elderly men and women. With increasing life expectancy, sarcopenia is a major public health concern in the geriatric societies (4).  Approximately 7 to 27.8% of the United States (US) men and 10 to 19.3% of US women, aged ≥ 60 years, suffer from sarcopenia (5-6), with increasing prevalence of sarcopenia in persons over 80 years of age (50%) (7) and in some cancer patients (68.9%) (8).  Estimated medical costs associated with sarcopenia in the US is about 18 billion a year (5).  Since effective clinical treatments for sarcopenia in the elderly populations are limited, preserving muscle mass and muscle strength at younger and middle ages is imperative to avoid the burden of this disease.
Skeletal muscle mass decreases about 40% between the ages of 20 and 80 years (9) with an annual decreasing rate of 1 to 2% after 50 years of age (10).  Notably, persons with skeletal muscle loss and excess fat are at greater risk of physical disability and mortality (11).  Although the primary causes of sarcopenia still remain unknown, early detection and subsequent treatment of sarcopenia is a key to prevent sarcopenia-related disability and mortality.
To address sarcopenia prevention strategies, establishing an accurate definition of sarcopenia should be in the first place.  Baumgartner et al. first proposed cut-points to define sarcopenia using low muscle mass (12).  Several investigators have shown that low muscle mass is associated with disability (2,12) and mortality (13).  Other investigators have also shown that low muscle strength, not low muscle mass, is associated with disability (14) and mortality (15).  Currently, sarcopenia has been defined as the combination of low muscle mass and weakness or slowness (16-20).  However, the definition of sarcopenia still remains in dispute worldwide. The European Working Group on Sarcopenia in Older People (EWGSOP) (16) and the Asian Working Group for Sarcopenia (AWGS) consensus panels have defined sarcopenia using the combination of low muscle mass and low muscle function (17).  The International Working Group on Sarcopenia (IWGS) (18) and the Society of Sarcopenia, Cachexia and Wasting Disorders (SCWD) (19) have defined sarcopenia using the combination of low muscle mass and low physical performance. The Foundation for the National Institutes of Health (FNIH) (20) defined sarcopenia using the combination of low muscle mass and low muscle strength. These inconsistent guidelines may lead to confusion to the public and clinical settings as a screening tool to determine sarcopenia patients.
From the methodological perspectives, the definition of sarcopenia should represent muscle quality, muscle strength per unit of muscle mass, rather than muscle mass or muscle strength. Some investigators have shown that intermuscular fat increases by 35.5-74.6% in men and 16.8-50% in women with aging (21), and an increase in fat mass is positively associated with muscle mass and muscle strength (22).  Thus, the greater muscle strength or muscle mass associated with increment in fat may lack muscle quality.  Although few studies have shown that muscle quality is a better indicator of functional capacity as compared with muscle mass or muscle strength (23), there is no standardized method to define sarcopenia using muscle quality.  To fill this gap, we investigated the cut-points to define sarcopenia using the muscle quality indexes (MQIs) in the young reference adults.

 

Methods

Study Participants

Fifty young male and female adults (ages 20-29 years; m = 30, f = 20) and forty elderly male and female adults (ages 60 to 79 years; m = 16; f = 24) were recruited for the present study.  The study was advertised by fliers, online posts, and University announcements within the Downtown Phoenix area.  For the healthy young reference group, inclusion criteria were aged 20 to 29 years, body mass index (BMI) <30 kg/m2 (weight in kilograms divided by height in meters squared), ability to perform physical activity assessed by online physical activity readiness questionnaire (PAR-Q), no pregnant, no personal history of chronic diseases, and not taking any hypoglycemic and hypertensive medications. For the elderly persons, inclusion criteria were aged 60 or more, ability to perform physical activity assessed by online PAR-Q, with no personal history of heart disease, stroke, or cancer.  Written informed consent was obtained from all subjects prior to study participation. The study was approved by the Institutional Review Board at Arizona State University.  All participants were given a detailed description of the protocol prior to their participation.

Measurement Procedure

Body height and weight were measured using a standardized physician’s scale. Dual-energy X-ray absorptiometry (DXA) was used to assess body composition, and arm and leg skeletal muscle mass by a licensed technician (Lunar iDXA, GE Healthcare, Madison, WI). Appendicular skeletal muscle mass (SMS) was computed by combining lean tissues in both arms and legs, and relative muscle mass was computed as SMS divided by height in meters squared (AMS) or SMS divided by body mass index (AMSBMI).
The grip strength was measured using Takei Physical Fitness Test dynamometer (kg).  The dominant hand was used with the subject standing and their arm at a position parallel to the floor. Grip strength was measured twice, and the average of two test scores was used for analysis. The leg strength was measured by isometric knee extension test (1 set of 3 repetitions) at an angle of 60 degrees using the CSMI Humac Norm Dynamometer test (Nm). An average of the highest two performance scores was used for analysis.
Muscle quality in the arm (MQIArm, kg/kg) was calculated as the grip strength (STRArm, kg), right arm, divided by the lean mass in the right arm (LMArm, kg).  Muscle quality in the leg (MQILeg, Nm/kg) was calculated as the isometric leg strength (STRLeg, Nm), right leg, divided by lean mass in the right leg (LMLeg, kg). Total muscle quality (MQITotal) was computed as the combination of MQIArm and MQILeg. Standardized MQI (MQIStd) was computed as the combination of z-scores in both MQIArm and MQILeg.  In the elderly persons, MQIStd was computed by the combination of z-scores in both MQIArm and MQILeg, using the sex-specific means and SDs from the healthy young reference group.

Statistical Analysis

General linear models were used to investigate mean differences for anthropometric, clinical measures, relative muscle mass and muscle quality indexes between men and women after adjustment for age and race. The normality assumptions for all outcome measures were justified by Shapiro-Wilk test or Kolmogorov-Smirnov test.  Sex-specific cut-points for ASM, ASMBMI, MQIArm, MQILeg, MQITotal, and MQIStd were computed as >1 SD, 1 SD≥ to >2 SD, and ≤2 SD below from the mean values in the young reference group. Sarcopenia was defined as ≤2 SD below from the mean values in the young reference group. We also examined the sex- and race-adjusted partial Pearson correlations among of muscle mass, muscle strength, and muscle quality in both young and elderly adults, respectively.  All statistical procedures were performed by Statistical Analysis Systems (SAS 9.4) software (SAS Institute, Cary, NC).

 

Results

In the young reference group, as shown in Table 1, men had greater BMI, SBP, grip strength, STRLeg, LMArm, and LMLeg than did women after adjustment for age and race (all p<0.001). There were no statistical gender differences in DBP, MQILeg, MQITotal, and MQIStd (all p>0.10), while women had greater MQIArm than did men (p<0.001). In the elderly persons, men had greater grip strength, LMArm, STRLeg, LMLeg, MQIStd than did women (all p<0.02). There were no statistical gender differences in BMI, SBP, DBP, MQIArm, MQILeg, and MQITotal (all p>0.35).

Table 1 Characteristics of the study participants in young and elderly adults

Table 1
Characteristics of the study participants in young and elderly adults

*Values are means. †Adjusted for age and race. LMArm, a lean mass in the arm; LMLeg, a lean mass in the leg; STRLeg, leg strength; MQIArm, muscle quality in the arm; MQILeg, muscle quality in the leg; MQITotal, a combination of MQIArm and MQILeg; MQIStd, a standardized MQI.

 

The sex-specific relative muscle mass (ASM and ASMBMI) and MQI (MQIArm, MQILeg, MQITotal, and MQIStd) cut-points are shown in Table 2.  The ASM, ASMBMI, and MQI cut-points were classified as normal, low, and poor categories, corresponding to >1 SD, 1 SD≥ to >2 SD and ≤2 SD below from the sex-specific mean values in the young reference group.  “Poor” categories were classified as sarcopenia.  The cut-points for sarcopenia using ASM and ASMBMI in men were ≤7.75 kg/m2 and ≤0.96, and in women were ≤5.69 kg/m2 and ≤0.71, respectively.  The cut-points for sarcopenia using MQIArm, MQILeg, MQITotal, and MQIStd in men were ≤8.37, ≤12.07, 22.06, and <-3.35, and in women were ≤10.09, ≤13.97, 28.22, and <-2.25, respectively.

Table 2 Cut-points to define sarcopenia using relative muscle mass and muscle quality indexes in young men and women

Table 2
Cut-points to define sarcopenia using relative muscle mass and muscle quality indexes in young men and women

*Normal, low, and poor indicates >1 SD, 1 SD≥ to >2 SD, and ≤2 SD below from the sex-specific mean values in the reference group. ASM, appendicular skeletal muscle mass; ASMBMI, ASM divided by height in meters squared; MQIArm, muscle quality in the arm; MQILeg, muscle quality in the leg; MQITotal, total muscle quality; MQIStd, standardized muscle quality

 

In the elderly adults, the frequencies of sarcopenia using MQIArm, MQILeg, MQITotal, and MQIStd were 15% (n = 6), 27.5% (n = 11), 32.5% (n = 13), and 35% (n = 14), respectively.  The sex- and race-adjusted partial Pearson correlations among muscle mass, muscle strength, and muscle quality are shown in Table 3.  There was no association between muscle mass and muscle strength in both young (r = 0.19, p = 0.20) and elderly adults (r = 0.05, p = 0.75), but muscle mass was inversely associated with muscle quality in young (r = -0.48, p<0.001) and elderly adults (r = -0.73, p<0.001).  There was a moderate association between muscle strength and muscle quality in young (r = 0.62, p<0.001) and elderly persons (r = 0.46, p<0.001).

Table 3 Sex- and race-adjusted Pearson partial correlations among muscle mass, muscle strength, and muscle quality in young and elderly adults

Table 3
Sex- and race-adjusted Pearson partial correlations among muscle mass, muscle strength, and muscle quality in young and elderly adults

Muscle mass, a combined relative muscle mass in both arm and leg; Muscle strength, a combined z-scores of muscle strength in both arm and leg; Muscle quality, a combined z-scores of muscle quality in both arm and leg. *p<0.001

 

Discussion

Although the rising trend in the prevalence of sarcopenia and disabilities is a major public health concern in the US (5-6), the accurate definition of sarcopenia still remains in controversial.  To our knowledge, we first define sarcopenia using MQI cut-points (MQIArm, MQILeg, MQITotal, and MQIStd) based on young reference group.  Several investigators have proposed muscle quality index or muscle power index using the ratio of muscle strength to muscle mass or the ratio of muscle power to muscle mass (24-25).  Barbat-Artigas et al. (24) proposed MQI cut-points using the ratio of grip strength to total skeletal muscle mass (kg/SMkg) based on young reference population.  Using this ratio, they classified “poor” MQI cut-points in men and women as ≤1.36 and ≤1.35 kg/SMkg.  The Concord Health and Ageing in Men Project (CHAMP) proposed lower and upper extremity muscle quality scores based on the lowest 20% of the distribution in men aged 70 to 90 years (25).  Other investigators have also proposed muscle power index using the ratio of muscle power (W) to total skeletal muscle mass (SMkg) (24) or the ratio of muscle power to time (26).  However, the feasibility of these indices in clinical settings as a screening tool to detect sarcopenia has not been well documented.
Muscle mass, muscle strength, and muscle quality are associated with physical function and disability, all of these are important factors to define sarcopenia (12, 14, 23, 24-25).  The muscle quality represents muscle’s ability to function, which is the best marker of functional capacity when compared with muscle mass or muscle strength (23).  The CHAMP study also showed that muscle quality or muscle strength, not muscle mass, was a strong predictor of physical function and disability (25).  Several International Working Groups have defined sarcopenia using the combination of low muscle mass and weakness or slowness (16-20).  Defining sarcopenia using muscle mass and muscle weakness may have some limitations without considering myosteatosis (intermuscular and intramuscular adipose tissue).  For instance, muscle mass or muscle strength with myosteatosis is not a good indicator of functional capacity because aging is positively associated with an increase in fatty infiltration of muscle tissue (27-28).  Some investigators have also shown that elderly men had about 59-127% more fat in quadriceps and hamstrings than did young men (27), with an annual increase of intramuscular fat by 18% (28).  Interestingly, an increase in fat mass is positively associated with muscle mass and muscle strength but is negatively associated with muscle quality (22).  In fact, a greater muscle mass or muscle strength with excess fat may lack muscle quality, which may misclassify sarcopenic patients to nonsarcopenic patients. Increasing muscle strength per unit of muscle mass, not by accumulating fat mass, is associated with muscle quality. Our findings also show that muscle mass is inversely associated with muscle quality in young and elderly persons, which is consistent with the findings from the US general population and the French women study (29-30).  The muscle quality is a strong surrogate marker for sarcopenia because it quantifies the function of muscle mass and muscle strength as a single unit.  Further studies are needed to determine whether muscle quality is a better marker for physical disability and mortality as compared with the combination of low muscle mass and low muscle function, which defined sarcopenia by International Working Groups (16-20).  Also, more studies are needed to justify the optimal cut-points for MQIs, muscle strength, and muscle mass in relation to disability and mortality.
A strength of this study is that the MQIs are based on young healthy reference group.  Our cut-points to define sarcopenia using ASM in men were slightly higher (0.5 kg/m2) than those cut-points by Baumgartner et al. (12), but our women’s cut-points were similar with the EWGSOP (16).  In the ASMBMI cut-points, we observed that our ASMBMI cut-points were greater than the FNIH cut-points in both men and women, which may be due to methodological differences defining sarcopenia.  For instance, the FNIH cut-points to define sarcopenia for ASMBMI were based on the elderly people (aged 70-90 years) using the mean values of the lowest 20% distribution, whereas our cut-points to define sarcopenia were based on young reference group (aged 20-29 years) using <2 SD from the mean values.  Another strength of our study is that we used DXA, a criterion method, to estimate lean mass in both arms and legs. A limitation of our study is that our findings may limit generalizability due to small sample size.  Further studies are needed to define MQI cut-points with a large sample size across different race and gender groups.
In summary, muscle quality is a significant risk factor for disability and mortality.  Based on healthy young reference men and women, we establish a new definition of sarcopenia using muscle quality indexes.  At the very least, our muscle quality indices may still be a role as a screening tool in detecting sarcopenia across individual and population level.

 

Acknowledgements: This study was supported by Mayo-Arizona State University Obesity Solution Grant.  The authors thank the graduate students from the ASU and study participants for their important contributions.

Conflict of Interest: None

Ethical standard: This study was performed in accordance with the ethical standards by the Arizona State University review board and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.

 

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