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Impact of 16 weeks of Exercise and Protein Supplementation on Functional-Physical Fitness of Dwelling-Institutionalised Elders
Abstract
Background: Ageing is a natural, progressive and irreversible process characterized by morphological, psychological, functional, biochemical and nutritional changes. Physical inactivity (PI) is a factor that contributes to the starting of mass and muscle function decline in the elderly, often related to sarcopenia and physical frailty. Combined to protein nutritional intervention, exercise appears as an effective way to prevent muscle mass and physical fitness decline. In addition, the elderly population has difficulty in maintaining adequate protein nutrition and are the least involved in systematic exercise programs. This exploratory study was conducted to understand the isolated and combined effects of a 16-weeks of branched chain aminoacids (BCAA) supplementation (BS) and muscle strength exercise program (MSE) on functional-fitness performance in octogenarians. Methods: The sample consisted of 18 participants aged 82.97±8.05 years old, institutionalized in social care centres. They were divided into two groups: group 1 (MSE+BS, n=10); group 2 (BS, n= 8). Group 1 performed an elastic band strength exercise program carried out during 16-weeks together with BCAA supplementation consisting of ingesting 0.21g/kg/day of unflavoured powder diluted into 200mls of water, immediately after exercise. Group 1 did only the BCAA supplementation. To evaluate the functional capacity of the elderly, the short battery of tests SPPB was used in the initial and final intervention evaluation. Results: After 16 weeks, group 1 (MSE+BS) showed a significant increase in all the SPPB tests performance, particularly in the test consisting in rising from a chair and seating down for 5 times. The SB group showed only a short decrease in the time taken to perform the 3 meters walk test (p < .05). Conclusion: Our study revealed that exercise plus supplementation with BCAAs was able to improve physical fitness function, while BCAA supplementation alone had limited effects. Satisfactory results in physical function could be explained by the added effects of exercise and BCAA supplementation on the protein synthesis effect.
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Purpose of Review
Sarcopenia results in disability and negatively impacts older adults’ ability to live independently. The purpose of this review is to summarize the recent literature regarding the effectiveness of exercise and nutritional supplementation as a treatment for sarcopenia.
Recent Findings
A number of recent studies demonstrated improvements in muscle mass and function in sarcopenic adults through resistance training and combination resistance+aerobic exercise training. Variability in program design, duration, and intensity leads to inconsistent findings in the literature. The addition of protein supplementation to resistance training appears to lead to more consistent improvements in muscle mass and function in sarcopenia.
Summary
Appropriately dosed exercise and dietary interventions improve muscle mass and function. Whether sarcopenia can be “cured” through these interventions, or if improved function and prevention of further declines should be the treatment goal, is unknown. Future research is needed to optimize the exercise prescription for treatment of sarcopenia.
Objective
To counteract muscle mass, muscle strength and power loss during aging, and to study age-related change of neuromuscular manifestation of fatigue in relation to nutritional supplementation.
Design
randomized controlled double-blind study.
Setting
Twice-daily consumption for 12 weeks of an Essential Amino Acids (EAA)-based multi-ingredient nutritional supplement containing EAA, creatine, vitamin D and Muscle Restore Complex®.
Participants
38 healthy elderly subjects (8 male, 30 female; age: 68.91±4.60 years; body weight: 69.40±15.58 kg; height: 1.60±0.09 m) were randomized and allocated in supplement (SUPP) or placebo (PLA) group.
Mean Measurements
Vitamin D blood level; Appendicular Lean Mass (ALM); Visceral Adipose Tissue (VAT); Maximal Voluntary Contraction (MVC) and Peak Power (PP); myoelectric descriptors of fatigue: Fractal Dimension and Conduction Velocity initial values (FD iv, CV iv), their rates of change (FD slopes, CV slopes) and the Time to perform the Task (TtT).
Mean Results
Significant changes were found in SUPP compared to baseline: Vitamin D (+8.73 ng/ml; p<0.001); ALM (+0.34 kg; p<0.001); VAT (-76.25 g; p<0.001); MVC (+0.52 kg; p<0.001); PP (+4.82 W; p<0.001). Between group analysis (SUPP Vs. PLA) showed improvements: vitamin D blood levels (+11,72 ng/ml; p<0.001); Legs FFM (+443.7 g; p<0.05); ALM (+0.53 kg; p<0.05); MVC (+1.38 kg; p<0.05); PP (+9.87 W; p<0.05). No statistical changes were found for FD iv, CV iv, FD and CV slopes and TtT, either compared to baseline or between groups. Significant correlations between mean differences in SUPP group were also found.
Conclusion
The study demonstrates that in healthy elderly subjects an EAA-based multi-ingredient nutritional supplementation of 12 weeks is not effective to change myoelectric manifestation of fatigue and TtT failure but can positively affect muscle mass, muscle strength, muscle power and VAT, counterbalancing more than one year of age-related loss of muscle mass and strength.
Frailty syndrome is a medical condition that is characterised by a functional decline, usually from 65 years old on, and creates the need for assistance to perform daily living activities. As the population ages, the need for specialised geriatric care will increase immensely, and consequently, the need for specialised services for the care of these people will increase accordingly. From a nutritional point of view, to control or balance the nutritional status of residents will be essential in order to prevent sarcopenia and, consequently, frailty development. In this line, previous studies have highlighted the association among low energy intake, inadequate intake of protein and vitamin D, and an increased risk of frailty development. However, there is a lack of intervention studies on frail patients, especially in the realm of quality clinical trials. The few studies performed to date seem to indicate that there is a protective role of protein supplementation against frailty syndrome. In this regard, it is tempting to suggest daily 30 g protein supplements to prevent frailty. However, it is well established that excess protein can also be harmful; therefore, specific individual characteristics should be considered before prescribing these supplements. On the other hand, the relevance of other nutritional interventions, such as vitamin D, omega-3, and medium-chain triglycerides, is much more scarce in the literature. Therefore, we encourage the development of new clinical trials to carry out effective therapies to prevent frailty development.
Background:
The ongoing "Sarcopenia and Physical fRailty IN older people: multi-componenT Treatment strategies (SPRINTT)" randomized controlled trial (RCT) is testing the efficacy of a multicomponent intervention in the prevention of mobility disability in older adults with physical frailty & sarcopenia (PF&S). Here, we describe the procedures followed for PF&S case finding and screening of candidate participants for the SPRINTT RCT. We also illustrate the main demographic and clinical characteristics of eligible screenees.
Methods:
The identification of PF&S was based on the co-occurrence of three defining elements: (1) reduced physical performance (defined as a score on the Short Physical Performance Battery between 3 and 9); (2) low muscle mass according to the criteria released by the Foundation for the National Institutes of Health; and (3) absence of mobility disability (defined as ability to complete the 400-m walk test in 15 min). SPRINTT was advertised through a variety of means. Site-specific case finding strategies were developed to accommodate the variability across centers in catchment area characteristics and access to the target population. A quick "participant profiling" questionnaire was devised to facilitate PF&S case finding.
Results:
During approximately 22 months, 12,358 prescreening interviews were completed in 17 SPRINTT sites resulting in 6710 clinic screening visits. Eventually, 1566 candidates were found to be eligible for participating in the SPRINTT RCT. Eligible screenees showed substantial physical function impairment and comorbidity burden. In most centers, project advertisement through mass media was the most rewarding case finding strategy.
Conclusion:
PF&S case finding in the community is a challenging, but feasible task. Although largely autonomous in daily life activities, older adults with PF&S suffer from significant functional impairment and comorbidity. This subset of the older population is therefore at high risk for disability and other negative health-related events. Key strategies to consider for successfully intercepting at-risk older adults should focus on mass communication methods.
BACKGROUND/OBJECTIVES: Adequate protein intake is essential to retaining muscle and maintaining physical function, especially in the elderly, and L-Leucine has received attention as an essential amino acid (EAA) that enhances protein retention. The study’s aim was to compare the efficacy of EAAs mixtures on lean tissue mass (LTM) and functional performance (FP) in a healthy elderly population.
SUBJECTS/METHODS: Thirty-six subjects (65-75 years) volunteered to receive capsules with EAAs (Groups A, B containing 20% and 40% L-Leucine respectively) or placebo (Lactose containing 0% L-Leucine, Group C) for 12 weeks. The daily amount ranged from 11 to 21g (0.21 g.kg-1.d-1) and was taken into 2 equal dosages alongside food, morning and evening. Main outcomes measured pre- and post- intervention were LTM, and FP [30-second arm-curl-test (30-ACT); 30-second chair-stand-test (30-CST); 6-minute walk-test (6-WT); and handgrip strength]. Secondary outcomes included dietary intakes and physical activity.
RESULTS: Twenty-five subjects (11 male and 14 female) completed the study (Group A, n=8; Group B, n=8; Group C, n=9). Gains associated with medium effect sizes were noted in LTM (Group B, 1.1 ±1.1%, p=0.003) and FP [Group A in 30-CST (11.0±11.5%, p=0.02) and 6-WT (8.8±10.0%, p=0.02); Group B in 6-WT (5.8±6.6%, p=0.03) and a trend in 30-CST (13.2±16.0, p=0.06)]. Significant differences between groups were not observed in secondary outcomes.
CONCLUSIONS: Twice daily supplementation of EAAs containing 20% or 40% L-Leucine improved aspects of functional status and at the higher level improved LTM. Further work to establish change in a larger sample and palatable supplemental format is now required.
The increase rate of utilization of branched-chain amino acids (BCAA) by muscle is reduced to its plasma concentration during prolonged exercise leading to glycogen. BCAA supplementation would reduce the serum activities of intramuscular enzymes associated with muscle damage. To examine the effects of BCAA administration on fatigue substances (serotonin, ammonia and lactate), muscle damage substances (CK and LDH) and energy metabolism substances (FFA and glucose) after endurance exercise. Subjects (n = 26, college-aged males) were randomly divided into an experimental (n = 13, EXP) and a placebo (n = 13, CON) group. Subjects both EXP and CON performed a bout of cycle training (70% VO2max intensity) to exhaustion. Subject in the EXP were administrated BCAA (78ml/kg·w) prior to the bout of cycle exercise. Fatigue substances, muscle damage substances and energy metabolism substances were measured before ingesting BCAAs and placebos, 10 min before exercise, 30 min into exercise, immediately after exercise, and 30 min after exercise. Data were analyzed by two-way repeated measure ANCOVA, correlation and statistical significance was set at p < 0.05. The following results were obtained from this study; 1. In the change of fatigue substances : Serotonin in the EXP tended to decreased at the 10 min before exercise, 30 min into exercise, post exercise, and recovery 30 min. Serotonin in the CON was significantly greater than the EXP at the10 min before exercise and recovery 30. Ammonia in the EXP was increased at the 10 min before exercise, 30 min into exercise, and post exercise, but significantly decreased at the recovery 30min (p < 0.05). Ammonia in the CON was significantly lower than the EXP at the 10 min before exercise, 30 min into exercise, and post exercise (p < 0.05). Lactate in the EXP was significantly increased at the 30 min into exercise and significantly decreased at the post exercise and recovery 30 min. Lactate in the CON was significantly lower than the EXP at the post exercise (p < 0.05). 2. In the change of muscle damage substances : CK in the EXP was decreased at the 10 min before exercise and increased at the 30 min into exercise and then decreased at the post exercise and recovery 30 min. CK in the CON was greater than the EXP. LDH in the EXP was decreased at the 10 min before exercise and increased at the 30 min into exercise and then decreased at the post exercise and recovery 30 min. LDH in the CON was higher than the EXP. 3. In the change of energy metabolism substances :Glucose in the EXP tended to decrease at the 10 min before exercise, 30 min into exercise, post exercise and recovery 30 min. Glucose in the CON was significantly greater than the EXP at the recovery 30 min (p < .05). FFA in both EXP and CON was increased at the post exercise and recovery 30 min. % increase for FFA in the EXP was greater than the CON at the post exercise and recovery 30 min. 4. The relationship of the fatigue substances, muscle damage substances and energy metabolism substances after endurance exercise indicated strongly a positive relationship between LDH and ammonia and a negative relationship between LDH and FFA in the EXP. Also, there were a strong negative relationship between glucose and FFA and a positive relationship between glucose and serotonin in the EXP. There was a strong positive relationship between CK and LDH and a strong negative relationship between FFA and glucose in the CON. These results indicate that supplementary BCAA decreased serum concentrations of the intramuscular enzymes as CK and LDH following exhaustive exercise. This observation suggests that BCAA supplementation may reduce the muscle damage associated with endurance exercise.
The construct and concurrent validity of the Thera-Band Perceived Exertion Scale for Resistance Exercise with elastic bands (EB) was examined. Twenty subjects performed two separate sets of 15 repetitions of both frontal and lateral raise exercise over two sessions. The criterion variables were myoelectric activity and heart rate. One set was performed with an elastic band grip width that permitted 15 maximum repetitions in the selected exercise, and another set was performed with a grip width 50% more than the 15RM grip. Following the final repetition of each set, active muscle (AM) and overall body (O) ratings of perceived exertion (RPE) were collected from the Thera-Band® resistance exercise scale and the OMNI-Resistance Exercise Scale of perceived exertion with Thera-Band® resistance bands (OMNI-RES EB). Construct validity was established by correlating the RPE from the OMNI-RES EB with the Thera-Band RPE scale using regression analysis. The results showed significant differences (p ≤ 0.05) in myoelectric activity, heart rate, and RPE scores between the low- and high-intensity sets. The intraclass correlation coefficient for active muscles and overall RPE scale scores was 0.67 and 0.58, respectively. There was a positive linear relationship between the RPE from the OMNI-RES EB and the Thera-Band scale. Validity coefficients for the RPE AM were r2 = 0.87 and ranged from r2 = 0.76 to 0.85 for the RPE O. Therefore, the Thera-Band Perceived Exertion Scale for Resistance Exercise can be used for monitoring elastic band exercise intensity. This would allow the training dosage to be better controlled within and between sessions. Moreover, the construct and concurrent validity indicates that the OMNI-RES EB measures similar properties of exertion as the Thera-Band RPE scale during elastic resistance exercise.
New evidence shows that older adults need more dietary protein than do younger adults to support good health, promote recovery from illness, and maintain functionality. Older people need to make up for age-related changes in protein metabolism, such as high splanchnic extraction and declining anabolic responses to ingested protein. They also need more protein to offset inflammatory and catabolic conditions associated with chronic and acute diseases that occur commonly with aging. With the goal of developing updated, evidence-based recommendations for optimal protein intake by older people, the European Union Geriatric Medicine Society (EUGMS), in cooperation with other scientific organizations, appointed an international study group to review dietary protein needs with aging (PROT-AGE Study Group). To help older people (>65 years) maintain and regain lean body mass and function, the PROT-AGE study group recommends average daily intake at least in the range of 1.0 to 1.2 g protein per kilogram of body weight per day. Both endurance- and resistance-type exercises are recommended at individualized levels that are safe and tolerated, and higher protein intake (ie, ≥1.2 g/kg body weight/d) is advised for those who are exercising and otherwise active. Most older adults who have acute or chronic diseases need even more dietary protein (ie, 1.2-1.5 g/kg body weight/d). Older people with severe kidney disease (ie, estimated GFR <30 mL/min/1.73m(2)), but who are not on dialysis, are an exception to this rule; these individuals may need to limit protein intake. Protein quality, timing of ingestion, and intake of other nutritional supplements may be relevant, but evidence is not yet sufficient to support specific recommendations. Older people are vulnerable to losses in physical function capacity, and such losses predict loss of independence, falls, and even mortality. Thus, future studies aimed at pinpointing optimal protein intake in specific populations of older people need to include measures of physical function.
Total, single repetition and contraction-phase specific (concentric and eccentric) time-under-tension (TUT) are important exercise-descriptors, as they are linked to the physiological and clinical response in exercise and rehabilitation.
To investigate the validity and reliability of total, single repetition, and contraction-phase specific TUT during shoulder abduction exercises, based on data from a stretch-sensor attached to an elastic exercise band.
A concurrent validity and interrater reliability study with two raters was conducted. Twelve participants performed five sets of 10 repetitions of shoulder abduction exercises with an elastic exercise band. Exercises were video-recorded to assess concurrent validity between TUT from stretch-sensor data and from video recordings (gold standard). Agreement between methods was calculated using Limits of Agreement (LoA), and the association was assessed by Pearson correlation coefficients. Interrater reliability was calculated using intraclass correlation coefficients (ICC 2.1).
Total, single repetition, and contraction-phase specific TUT - determined from video and stretch-sensor data - were highly correlated (r>0.99). Agreement between methods was high, as LoA ranged from 0.0 to 3.1 seconds for total TUT (2.6% of mean TUT), from -0.26 to 0.56 seconds for single repetition TUT (6.9%), and from -0.29 to 0.56 seconds for contraction-phase specific TUT (13.2-21.1%). Interrater reliability for total, single repetition and contraction-phase specific TUT was high (ICC>0.99). Interrater agreement was high, as LoA ranged from -2.11 to 2.56 seconds for total TUT (4.7%), from -0.46 to 0.50 seconds for single repetition TUT (9.7%) and from -0.41 to 0.44 seconds for contraction-phase specific TUT (5.2-14.5%).
Data from a stretch-sensor attached to an elastic exercise band is a valid measure of total and single repetition time-under-tension, and the procedure is highly reliable. This method will enable clinicians and researchers to objectively quantify if home-based exercises are performed as prescribed, with respect to time-under-tension.
A short battery of physical performance tests was used to assess lower extremity function in more than 5,000 persons age 71 years and older in three communities.
Balance, gait, strength, and endurance were evaluated by examining ability to stand with the feet together in the side-by-side, semi-tandem, and tandem positions, time to walk 8 feet, and time to rise from a chair and return to the seated position 5 times.
A wide distribution of performance was observed for each test. Each test and a summary performance scale, created by summing categorical rankings of performance on each test, were strongly associated with self-report of disability. Both self-report items and performance tests were independent predictors of short-term mortality and nursing home admission in multivariate analyses. However, evidence is presented that the performance tests provide information not available from self-report items. Of particular importance is the finding that in those at the high end of the functional spectrum, who reported almost no disability, the performance test scores distinguished a gradient of risk for mortality and nursing home admission. Additionally, within subgroups with identical self-report profiles, there were systematic differences in physical performance related to age and sex.
This study provides evidence that performance measures can validly characterize older persons across a broad spectrum of lower extremity function. Performance and self-report measures may complement each other in providing useful information about functional status.
Unlabelled:
The criterion variables were total weight lifted (Wttot ) determined separately for women and men during BC and KE, and blood lactic acid concentration ([Hla]) determined for a combined female ( N = 10) and male ( N = 10) subset during BC. Subjects performed three separate sets of 4, 8, and 12 repetitions for BC and KE at 65% one-repetition maximum. Rating of perceived exertion for the active muscles (RPE-AM) was measured during the mid and final repetition and RPE for the overall body (RPE-O) during the final repetition. : For both female and male groups across the three sets: (a) RPE-AM ranged from 3.6 to 8.2 for BC and 5.1 to 9.6 for KE and (b) RPE-O ranged from 2.4 to 6.7 for BC and 4.2 to 7.6 for KE. Positive linear regressions ranged from r = 0.79 to 0.91 ( P < 0.01) between Wttot and RPE-AM (mid), RPE-AM (final), and RPE-O for both BC and KE in both sex groupings. A positive ( P < 0.01) linear regression was found between [Hla] and RPE-AM (final) (r = 0.87) during BC. RPE did not differ between women and men at any measurement point within each set for BC and KE. RPE-AM (final) was greater ( P < 0.01) than RPE-O in the three sets of BC and KE.
Conclusion:
Findings provided concurrent validation of the OMNI-RES to measure RPE for the active muscle and overall body in young recreationally trained female and male weight lifters performing upper- and lower-body resistance exercise.
Various modalities of exercise have been demonstrated to improve physical function and quality of life in older adults. Current guidelines stress the importance of multi-modal exercise for this cohort, including strengthening exercises, cardiovascular, flexibility and balance training. There is a lack of evidence, however, that simultaneously prescribed doses and intensities of strength, aerobic, and balance training in older adults are both feasible and capable of eliciting changes in physical function and quality of life.
A comprehensive, systematic database search for manuscripts was performed. Two reviewers independently assessed studies for potential inclusion. Physical and functional performance outcomes were extracted. The relative effect sizes (ES) were calculated with 95% confidence intervals.
Fifteen studies were included totalling 2,149 subjects; the mean cohort age ranging from 67 +/- 8 to 84 +/- 3 years. A low mean relative ES for strength was seen across the reviewed studies. Only six of the eleven studies that included balance measurements found a significant improvement in balance compared to controls. Aerobic fitness was seldom measured or reported. Five out of the six studies investigating fall rates showed a significant reduction. Functional and quality of life measures generally did not improve with exercise.
Multi-modal exercise has a positive effect on falls prevention. The limited data available suggests that multi-modal exercise has a small effect on physical, functional and quality of life outcomes. Future research should include robustly designed trials that involve multi-modal exercise at individually prescribed intensities based on doses found to be effective in single-modality studies.
Senescent cells drive ageing and the associated loss in health and lifespan. Whether this is mediated by systemic signalling remained unclear. Recently, Xu et al. [1] (Nat. Med. 2018;24:1246–1256) answered this question by injecting senescent cells into young mice and observing a long-lasting increase in frailty and mortality.
Objective:
Protein supplementation increases gains in lean body mass following prolonged resistance-type exercise training in frail older adults. We assessed whether the greater increase in lean body mass can be attributed to muscle fiber type specific hypertrophy with concomitant changes in satellite cell (SC) content.
Design:
A total of 34 frail elderly individuals (77 ± 1 years, n = 12 male adults) participated in this randomized, double-blind, placebo-controlled trial with 2 arms in parallel.
Intervention:
Participants performed 24 weeks of progressive resistance-type exercise training (2 sessions per week) during which they were supplemented twice-daily with milk protein (2 × 15 g) or a placebo.
Methods:
Muscle biopsies were taken at baseline, and after 12 and 24 weeks of intervention, to determine type I and type II muscle fiber specific cross-sectional area (CSA), SC content, and myocellular characteristics.
Results:
In the placebo group, a trend for a 20% ± 11% increase in muscle fiber CSA was observed in type II fibers only (P = .051), with no increase in type I muscle fiber CSA. In the protein group, type I and II muscle fiber CSA increased by 23% ± 7% and 34% ± 10% following 6 months of training, respectively (P < .01). Myonuclear domain size increased over time in both groups and fiber types (P < .001), with no significant differences between groups (P > .05). No changes in myonuclear content and SC contents were observed over time in either group (both P > .05). Regression analysis showed that changes in myonuclear content and domain size are predictive of muscle fiber hypertrophy.
Conclusions:
Protein supplementation augments muscle fiber hypertrophy following prolonged resistance-type exercise training in frail older people, without changes in myonuclear and SC content.
This study assessed the efficacy of supplemented essential amino acids on depressive symptoms, nutrition, muscle function, daily physical activity, and health-related quality of life (HRQoL) of institutionalized elderly patients.
Forty-one patients (58.5% women; mean age 79.8 yrs) with sequelae of coronary artery disease (73%), femoral fracture (34%), were randomly assigned to receive oral essential amino acids 4 gr 2 times a day for 8 weeks or isocaloric placebo. Before randomization and 8 weeks after the protocol started, the following variables were measured: depressive symptoms (Geriatric Depression Scale, GDS), nutritional panel (Mini Nutritional Assessment, MNA; serum albumin and prealbumin levels), muscle strength (Hand Grip, HG), Activity Daily Life (ADL), Quality of Life (SF-36, HRQoL) and amino acid profile.
Compared with the placebo group, EAA patients improved nutrition (MNA score 22.6 ± 1.5 post vs 21.8 ± 1.6 pre; p < 0. 04, albumin g/dl 4.04 ± 0.35 post vs 3.88 ± 0.3 pre; p < 0.01), GDS(score 10.3 ± 1.75 post vs 13.85 ± 3.37 pre; p < 0.001), HG (Kg 19.75 ± 1.7 post vs 18.68 ± 1.36 pre; p = 0.001), ADL (p < 0.04) and both physical and mental components of SF-36 (p < 0.002).
Oral supplementation with essential amino acids improved several determinants of quality of life in institutionalized elderly patients, including depressive symptoms, nutrition, muscle function and daily life activity.
There is a great demand for perceptual effort ratings in order to better understand man at work. Such ratings are important complements to behavioral and physiological measurements of physical performance and work capacity. This is true for both theoretical analysis and application in medicine, human factors, and sports. Perceptual estimates, obtained by psychophysical ratio-scaling methods, are valid when describing general perceptual variation, but category methods are more useful in several applied situations when differences between individuals are described. A presentation is made of ratio-scaling methods, category methods, especially the Borg Scale for ratings of perceived exertion, and a new method that combines the category method with ratio properties. Some of the advantages and disadvantages of the different methods are discussed in both theoretical-psychophysical and psychophysiological frames of reference.
Protein and amino acid requirements in human nutrition
WHO/FAO/UNU Expert Consultation. (2007). Protein and amino acid requirements in
human nutrition. World Health Organization Technical Report Series, (935), 1-265.
https://doi.org/ISBN 92 4 120935 6