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Low-Load Resistance Training Performed to Muscle Failure or Near Muscle Failure Does Not Promote Additional Gains on Muscle Strength, Hypertrophy, and Functional Performance of Older Adults

Bergamasco, João Guilherme Almeida1; da Silva, Deivid Gomes1; Bittencourt, Diego Fernandes1; de Oliveira, Ramon Martins1; Júnior, José Carlos Bonjorno2; Caruso, Flávia Rossi3; Godoi, Daniela4; Borghi-Silva, Audrey3; Libardi, Cleiton Augusto1

Author Information
Journal of Strength and Conditioning Research: May 2022 - Volume 36 - Issue 5 - p 1209-1215
doi: 10.1519/JSC.0000000000003632
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Abstract

Introduction

The aging process is associated with progressive declines in muscle strength and mass (8). Such reductions may lead to functional impairments, increased risk of falling, and difficulties in performing activities of daily living (1).

A widely recommended strategy to mitigate the aging-related alterations in muscle morphology and functional performance is the regular practice of resistance training (RT) (1). It is known that RT may maximize muscle strength gains and hypertrophy even using low-load protocols (e.g., <50% of 1 repetition maximum [1RM]), as long as the exercise is performed to muscle failure (20,36). However, exercising to the point of muscle failure acutely exacerbates blood pressure raises (14). In addition, a potential issue with the performance of continuous RT to muscle failure is that it may increase the potential for overtraining and musculoskeletal injuries (32). In fact, the American College of Sports Medicine recommends nonfailure RT protocols for older adults, which should be performed until a substantial fatigue is installed (1,2). In this sense, our group demonstrated that RT-induced muscle strength gains and hypertrophy are similar between failure vs. nonfailure protocols in young individuals (i.e., the point in which subjects voluntarily interrupted the exercise before muscular failure), even with lower muscle fatigue (i.e., lower decrease in performance throughout the sets) and number of repetitions induced by nonfailure protocols (10,20). In fact, it could represent an important strategy for older adults, once significant adaptations may be obtained through a nonfailure RT protocol. However, the effects of RT to muscle failure vs. nonfailure on neuromuscular adaptations and functional performance of older adults are so far poorly understood.

Although performing repetitions in proximity to muscle failure seems to be an interesting strategy for older adults, a significant training volume may be produced (i.e., number of repetitions) (20), which might not be aligned to the recommendations for older adults in early stages of RT (2). In this sense, another nonfailure RT strategy that may represent an attractive strategy for previously untrained older individuals is the application of low loads with a fixed low number of repetitions (i.e., far from muscle failure). It was demonstrated that an early interruption of the exercising sets, which would be relatively far from muscle failure, result in functional performance improvements, even without maximizing muscle strength gains and hypertrophy (1,25). However, it remains unclear whether the neuromuscular and functional performance adaptations promoted by low-load RT to voluntary interruption or with a fixed low number of repetitions could be comparable with low-load RT protocols performed to muscle failure in previously untrained older adults.

Thus, the aim of our study was to compare the effects of low-load RT protocols performed to muscle failure with nonfailure RT protocols performed to voluntary interruption or with a fixed low number of repetitions on muscle strength, hypertrophy, and functional performance of older adults. We hypothesized that the nonfailure protocols will be capable of promoting similar improvements in muscle strength, hypertrophy, and functional performance when compared with the muscle failure protocol.

Methods

Experimental Approach to the Problem

Initially, subjects underwent the vastus lateralis muscle cross-section area (CSA) measurement by ultrasound followed by the ballistic test. All subjects were first familiarized with the functional performance and 1RM tests. Seventy-two hours after familiarization, all tests were repeated and the results considered as baseline values (Pre). Thereafter, subjects were randomized in a balanced way into 1 of the 3 experimental protocols: low-load RT performed to muscle failure (FAI, n = 13, 4 men and 9 women), low-load RT performed to voluntary interruption (VOL, n = 12, 7 men and 5 women), and low-load RT performed with a fixed low number repetitions (FIX, n = 13, 7 men and 6 women). To ensure that the subjects assimilated the instructions provided for each of the training protocols, a familiarization session was performed before the beginning of the training sessions. After 72 hours later, the subjects started a 12-week training period, twice a week. At the week 6, 72 hours after the twelfth session, another 1RM test was performed to adjust the training loads. After 12 weeks (Post), all the assessments were performed after 72 hours from the last session, respecting the same order and time intervals.

Subjects

Forty-one older adults (men: n = 18, age: 67 ± 6 years [range: 60–77], height: 169 ± 6.5 cm, body mass 78.7 ± 9.3 kg, and body mass index (BMI): 27.7 kg/m2 and women: n = 23, age: 64 ± 3 years [range: 60–71], height: 157 ± 5.1 cm, body mass: 67 ± 9.2 kg, and BMI: 27.4 kg/m2; mean ± SD) were recruited for this study. After to receive the study information, all the subjects have signed informed consent and underwent a stress electrocardiogram test to verify any nonreported abnormality—conducted by a physician. To be included in the study, subjects should be absent from any RT activity in the last 6 months and refrain from any strenuous activities during the trial. Exclusion criteria involved cardiovascular diseases (e.g., blood vessel diseases, coronary artery disease, and arrhythmias), use of pacemaker, diabetes, and any musculoskeletal condition that could restrict the practice of RT with a high number of repetitions (i.e., FAI or VOL protocols). There were 3 dropouts during the study, one for health issues and other 2 for personal reasons. Thus, 38 subjects have completed all the training sessions and assessments. All procedures performed in our study were approved and were in accordance with the ethical committee of the Federal University of São Carlos (082446/2017) and with the Declaration of Helsinki.

Muscle Cross-Sectional Area

Cross-sectional area of vastus lateralis was measured through a B-mode ultrasonography imaging with a 7.5-MHz linear-array probe (Mysono U6 EX; Samsung, SP, Brazil). The subjects were asked to cease physical activity for at least 72 hours before the assessment. To begin, subjects lay down for 15 minutes to allow for fluid distribution. The images were collected at the midpoint of the right thigh, at 50% of the distance between the greater trochanter and the inferior border of the lateral epicondyle. At this point, legs were transversally marked every 2 cm from the medial to the lateral aspect of the vastus lateralis, to guide probe displacement. Surface gel was used to provide acoustic coupling without dermal deforming. After, sequential images were acquired aligning the top border of the probe with each of the marks after a middle-to-lateral orientation. After the digitalization, the images were sequentially opened and reconstructed in PowerPoint (Microsoft, Redmond, WA) in 2 different days, separated by 72 hours, and analyzed through the ImageJ software (15). The coefficient of variation (CV) and typical error (TE) between 2 procedures of image reconstruction separated by a 72-hours interval were 1.27% and 0.19 cm2, respectively.

Rate of Torque Development

The RTD was evaluated through a maximal ballistic voluntary isometric contraction (MBVIC) test, according to Libardi et al. (13). The settings of the isokinetic dynamometer (Biodex System 3; Biodex Medical Systems, Shirley, NY) were determined according to the technical specifications of the equipment. Before test, a general warm-up was performed in a cycle ergometer for 5 minutes at 60 rotations per minute and 25 watts. After, each subject was positioned vertically on the dynamometer's chair and firmly stabilized by 2 straps transversally displaced over their shoulders, 1 strap at the waist and 1 over the tested thigh. The knee center of rotation of the subject was aligned to the dynamometer center of rotation. The MBVIC test was performed at 60° from the horizontal plan. The accessory of the dynamometer was comfortably adjusted to the ankle of the subject, positioned over the medial and lateral malleoli. After the individualized positioning, the subjects performed a specific warm-up on the dynamometer, which consisted of 10 two-second submaximal isometric ballistic contractions, separated by 20-second intervals. After, 3 minutes after the warm-up period, subjects performed 4 MBVIC separated by 3-minute intervals. For the test, subjects were instructed to produce the maximum torque as fast and hard as possible, hold at maximal torque for 2 seconds, and relax as fast as possible. The curve was displayed to the subjects in real time to provide instantaneous feedback about the curve pattern, which should follow a “rectangular pattern” (i.e., the torque should increase as fast as possible, the maximal torque should be maintained, and torque decay should also follow a rapid pattern). Attempts were discarded when differed from the mentioned pattern. Strong verbal encouragement was provided in all the attempts. The chair adjustments were recorded to be repeated at the end of the 12 weeks. Data were analyzed through MATLAB 7.0 software, and RTD was calculated from the following formula: ∆T·∆t−1 (13).

Functional Performance: Chair Stand

Subjects started the test seated on a chair (43 cm) with their back against the chair and feet placed on a force platform (AccuGait, AMTI, Boston) (21). Subjects were instructed to keep arms crossed over their chest touching the contralateral shoulder and, as fast as possible, to stand up in a completely straight position and sit down for 5 consecutive times (17). The total time to complete this task was obtained through the Balance Clinic software (AMTI, Boston) and analyzed in MATLAB 7.0 software (Math Works Inc., Natick, MA) to increase timing accuracy. The CV and TE between tests were 3.84% and 0.45 seconds, respectively.

Habitual Gait Speed and Maximal Gait Speed

Subjects were instructed to walk through a 15-meter distance 2 consecutive times in 2 different gait speeds: habitual and maximal, both timed by a photocell (Speed Test Fit, Cefise Biotecnologia Esportiva, Sao Paulo, Brazil). The first and the last 2.5 meters were discarded as it was used as acceleration and deceleration periods, respectively. Results were composed by the mean of the 2 attempts in each of the gait speeds (31). The CV and TE between habitual gait speed (HGS) tests were 2.16% and 0.03 m·s−1, respectively and between maximal gait speed (MGS), 3.53% and 0.07 m·s−1, respectively.

Timed Up-and-Go

The subjects started the test seated with their back against an armed chair (43 cm), arms positioned over the lateral armrests, and feet placed over a force platform. After the starting command, subjects should stand up using the armrests, walk as fast as possible over a three-meters distance previously delimited, return and sit down with back against the seat (18). Time was measured and analyzed as described for the CS test. The CV and TE between tests were 3.69% and 0.31 seconds, respectively.

Maximal Dynamic Muscle Strength (1RM)

Maximal dynamic strength was assessed through bilateral 1RM tests, performed in 3 exercises at the same day in the following order: knee extension, leg press, and leg curl. In short, the subjects started with a general warm-up of 5 minutes on a cycle ergometer at 20 km·h−1. Subsequently, a specific warm-up of 8 repetitions at 50% of the estimated 1RM by a set of 3 repetitions at 70% of estimated 1RM was performed. Warm-up sets were separated by 2 minutes of rest. The 1RM test was composed by 5 attempts in each of the 3 exercises, with 3 minutes of rest between attempts and exercises (4). The results were presented as the sum of the 1RM values for all the 3 exercises. The CV and TE between tests were 1.7% and 1.0 kg in knee extension, 1.5% and 3.5 kg in leg press, and 2.2% and 0.8 kg in leg curl, respectively.

Resistance Training Protocols

All groups performed a lower-limb RT protocol in 3 exercises (knee extension, leg press, and leg curl) at 40% 1RM, twice a week. The same exercising order was respected for all protocols in all training sessions. For FAI, 3 sets were performed to muscle failure, which was defined as the point where the activated muscles are incapable of completing another repetition in the appropriate range of motion (11,20,29). For VOL, 3 sets were performed to voluntary interruption, which was defined as the point in which subjects voluntarily interrupted the exercise before muscular failure (20). Finally, FIX protocol consisted on 3 sets of 10 repetitions. There were respected 90 seconds of rest between sets for all the training protocols. To provide a whole-body training, all subjects performed a standardized upper-limb protocol, split in 2 RT routines: (A) chest press machine, lateral raises, and cable pushdowns and (B) lat pull-down, bicep curl, and sit-ups. The routines were alternately performed once a week after the lower-body RT protocol. There were performed 3 sets of 8–12 repetitions maximum in weight and machine exercises, while sit-ups were performed to muscle failure. Also with respect to the upper body, the load was adjusted through sets and RT bouts according to a repetition range (e.g., if the individuals performed more than 12 repetitions in a set, the load was increased to maintain maximum repetition range in the next set and the contrary was applied when the subjects were not able to complete at least 8 repetitions). A 90-second resting time was allowed between sets and exercises for the upper-body protocol.

Training Volume

Nrep (sets × repetitions) and total training volume (TTV) (sets × repetitions × load) were recorded in each session and presented as the sum of the 3 exercises. These data were used to calculate the area under curve (AUC) of all 24 training sessions. In addition, TTV was presented as the accumulation of the 24 training sessions. Rate of training progression (RTP) was analyzed considering Nrep and TTV at weeks 1 (W1), 6 (W6), and 12 (W12). Finally, to provide an indirect measurement of fatigue for VOL and FAI, Drep was calculated through the difference from the third and the first sets (Drep = third set − first set) (10,20).

Statistical Analyses

After a visual inspection, the normality of data was evaluated through Shapiro-Wilk test. One-way analysis of variance (ANOVA) was applied to compare baseline values (CSA, RTD, CS, HGS, MGS, timed up-and-go [TUG], and 1RM), Nrep AUC, TTV AUC, and Drep between protocols. A mixed model analysis was applied for CSA, RTD, CS, HGS, MGS, TUG, 1RM, and RTP), assuming protocols (FAI, VOL, and FIX) and time (Pre and Post [W1, W6, and W12 for RTP]) as fixed factors, and subjects as random factors. In case of significant F, Tukey adjustment was applied for multiple comparisons. The relative changes (%) were displayed on the tables as mean ± SD with 95% confidence intervals (CI). The effect size (ES) was calculated for all dependent variables using the changes from pre-training to post-training, and classified as small (<0.20), moderate (0.2–0.79), and large (>0.8 large) (7). The level of significance adopted was p ≤ 0.05. Statistical analyses were performed using SAS 9.3 software (SAS institute Inc., Cary, NC).

Results

Baseline Values

There were no significant differences in the baseline values for CSA, RTD, CS, HGS, MGS, TUG, and 1RM (p > 0.05).

Muscle Cross-Sectional Area

There were no main protocols, time, or interaction protocols vs. time effects in muscle CSA (p > 0.05; ES: FAI = 0.15 [small], VOL = 0.08 [small], FIX = 0.11 [small]) (Table 1).

Table 1 - Maximal dynamic strength (1RM), muscle cross-sectional area (CSA), and rate of torque development (RTD) at baseline (Pre) and after training (Post) for RT performed to failure (FAI), voluntary interruption (VOL), and fixed low number of repetitions (FIX).
Variable Protocol Pre Post Δ% (95% CI) [min–max]
1RM (kg) FAI 318.3 ± 116.3 393.0 ± 143.1* 23.5 (18.3 to 29.6) [8 to 44]
VOL 342.9 ± 93.7 423.0 ± 114.5* 23.3 (20.2 to 30.7) [16 to 41]
FIX 328.0 ± 107.2 397.8 ± 94.6* 21.3 (15.0 to 35.1) [4 to 61]
CSA (cm2) FAI 17.5 ± 6.0 18.4 ± 5.7 5.1 (−5.3 to 22.1) [−27 to 53]
VOL 18.0 ± 5.3 18.4 ± 3.7 2.0 (−8.0 to 20.8) [−22 to 44]
FIX 17.7 ± 4.4 18.1 ± 3.5 2.4 (−5.0 to 15.0) [−22 to 39]
RTD (N·m·s−1) FAI 565.7 ± 188.0 562.8 ± 205.0 −0.5 (−14.9 to 4.83) [−39 to 21]
VOL 605.4 ± 185.0 656.1 ± 141.0 8.4 (−2.5 to 26.9) [−29 to 49]
FIX 574.0 ± 186.6 635.8 ± 170.1 10.8 (1.8–32.8) [−21 to 61]
*Significantly different from Pre (main time effect, p < 0.05). Values presented as mean ± SD, mean percentage changes (Δ%), confidence interval (95% CI) in parenthesis, and range [min–max] in square brackets.

Rate of Torque Development

There were no main protocol, time, or interaction protocol vs. time effects in RTD (p > 0.05; ES: FAI = 0.01 [small], VOL = 0.31 [moderate], FIX = 0.35 [moderate]) (Table 1).

Functional Performance

There was a main time effect in CS (p = 0.001) and HGS (p = 0.036). The post hoc test revealed significant increases from pre-training to post-training for both CS (p = 0.001; ES: FAI = 0.52 [moderate], VOL = 0.88 [large], FIX = 0.32 [moderate]) and HGS (p = 0.036; ES: FAI = 0.12 [small], VOL = 0.43 [moderate], FIX = 0.55 [moderate]) (Table 1). There were no main protocol, time or interaction protocol vs. time effects for MGS (p > 0.05; ES: FAI = 0.16 [small], VOL = 0.17 [small], FIX = 0.31 [moderate]) and TUG (p = 0.055; ES: FAI = 0.35 [moderate], VOL = 0.81 [large], FIX = 0.03 [small]) (Table 2).

Table 2 - Functional tests at baseline (Pre) and after training (Post) for RT performed to failure (FAI), voluntary interruption (VOL), and fixed low number of repetitions (FIX).*
Variable Protocol Pre Post Δ % (95% CI) [min to max]
CS (s) FAI 11.5 ± 2.4 10.5 ± 1.1 −8.5 (−16.2 to 3.9) [−37 to 20]
VOL 12.1 ± 2.5 10.3 ± 1.5 −15.1 (−22.2 to −4.5) [−30 to 13]
FIX 11.3 ± 1.1 11.0 ± 1.1 −3.2 (−9.3 to 4.2) [−21 to 26]
HGS (m·s−1) FAI 1.3 ± 0.2 1.4 ± 0.2 2.5 (−3.1 to 7.0) [−9 to 21]
VOL 1.3 ± 0.1 1.4 ± 0.2 5.2 (−3.2 to 11.3) [−10 to 30]
FIX 1.3 ± 0.1 1.4 ± 0.1 5.7 (−14.9 to 2.2) [−7 to 43]
MGS (m·s−1) FAI 2.0 ± 0.2 2.0 ± 0.3 1.5 (−5.0 to 1.1) [−10 to 9]
VOL 2.0 ± 0.3 2.1 ± 0.3 2.6 (−6.3 to 10.2) [−24 to 22]
FIX 1.9 ± 0.2 1.9 ± 0.2 3.9 (−9.0 to 21.1) [−10 to 27]
TUG (s) FAI 8.0 ± 0.9 7.7 ± 0.8 −3.9 (−7.3 to 0.0) [−17 to 6]
VOL 8.2 ± 1.0 7.5 ± 0.7 −9.0 (−13.7 to −3.1) [−25 to 4]
FIX 7.9 ± 0.9 7.9 ± 0.9 −0.3 (−6.3 to 6.8) [−18 to 22]
*CI = confidence interval; CS = chair stand; TUG = timed up-and-go; RT = resistance training.
Significantly different from Pre (main time effect, p < 0.05). Values presented as mean ± SD, mean percentage changes (Δ%), confidence interval (95% CI) in parenthesis, and range [min to max] in square brackets.

Maximal Dynamic Strength (One Repetition Maximum)

There was a main time effect for 1RM (p < 0.0001). The post hoc test revealed significant increases from pre-training to post-training (p < 0.0001; ES: FAI = 0.57 [moderate], VOL = 0.79 [moderate], FIX = 0.69 [moderate]) (Table 1).

Training Volume

The 1-way ANOVA showed differences between protocols for Nrep AUC, TTV AUC, and Drep. FAI showed significantly greater Nrep AUC compared with VOL (p < 0.0001) and FIX (p < 0.0001). In addition, VOL demonstrated a significantly greater Nrep AUC than FIX (p < 0.0001) (Figure 1B). FAI performed a mean of 307 repetitions per session (considering knee extension, leg press, and leg curls together), while VOL performed 277 repetitions (90.2% of FAI) and FIX 90 repetitions (29.3% of FAI) (Figure 1A).

F1
Figure 1.:
Number of repetitions (Nrep) reported as area under the curves (AUC) (A), average of sessions (B), and rate of training progression (RTP) (C) for resistance training performed to failure (FAI), voluntary interruption (VOL), and fixed low number of repetitions (FIX). †Significantly different from W1 (p < 0.05). *Significantly different from FIX (p < 0.0001). #Significantly different from VOL (p < 0.0001). Values presented as mean ± SD.

Accumulated TTV was significantly greater (p < 0.0001) for FAI (391,595 ± 166,267 kg) and VOL (274,774 ± 118,209 kg) protocols compared with FIX (98,915 ± 29,430 kg) (Figures 2A and 2B). There were no significant differences between FAI and VOL (p > 0.05).

F2
Figure 2.:
Total training volume (TTV) reported as area under the curves (AUC) (A), average of sessions (B), and rate of training progression (RTP) (C) for resistance training performed to failure (FAI), voluntary interruption (VOL), and fixed low number of repetitions (FIX). †Significantly different from W1 (p < 0.0001); $Significantly different from W6 (p < 0.0001); *Significantly different from FIX (p < 0.0001). Values presented as mean ± SD.

For RTP of Nrep and TTV, a significant protocol vs. time interaction was observed (p < 0.0001; Figure 1C and p < 0.0001; Figure 2C, respectively). Regarding intraprotocol results, FAI and VOL significantly increased the RTP of Nrep from W1 to W6 (p < 0.0001 for both protocols) and W12 (p < 0.0001 for both protocols). In addition, there were no significant changes from W6 to W12 for any protocols (p > 0.05). Similarly, FAI and VOL significantly increased the RTP of TTV from W1 to W6 (p < 0.0001 for both protocols) and W12 (p < 0.0001, for both protocols). Furthermore, VOL significantly increased the RTP of TTV from W6 to W12 (p = 0.0002), while FAI showed no significant changes (p > 0.05). There were no significant changes in RTP of Nrep and TTV for FIX in any timepoint. For between-protocol results, RTP of Nrep was significantly higher for FAI and VOL than FIX in W6 (p = 0.0001; p = 0.0002, respectively) and W12 (p = 0.0012; p < 0.0001, respectively). Similarly, RTP of TTV was significantly higher for FAI and VOL than FIX in W6 (p = 0.0002; p = 0.0024, respectively) and W12 (p = 0.0002; p < 0.0001, respectively). There were no significant differences between FAI and VOL (p > 0.05) in any variables.

Finally, Drep was significantly greater for FAI (−5 ± 2 repetitions; −18%) and VOL (−3 ± 2 repetitions; −12.1%) compared with FIX (p < 0.0001). In addition, Drep was greater for FAI compared with VOL (p < 0.0001).

Discussion

To the best of our knowledge, this is the first study comparing the effects of low-load RT performed to muscle failure (FAI) vs. nonfailure (performed to voluntary interruption [VOL] or with a fixed low number of repetitions [FIX]) on muscle strength, hypertrophy, and functional performance in older adults. Our findings showed that low-load nonfailure RT protocols improve muscle strength and functional performance similarly to RT performed to muscle failure. In addition, increases in CSA may not be determinant to improve functional performance.

Regarding muscle strength, all protocols presented similar increase after 12 weeks of low-load RT. Curiously, the higher RTP of Nrep and TTV showed in FAI and VOL, as well as the higher Nrep accumulated by FAI in comparison with both nonfailure protocols (VOL and FIX) did not result in additional gains. These results are in accordance with other studies that did not show a dose-response relationship between TTV and Nrep and strength gains for older adults in early stages of RT (3,23). It is plausible that further increasing the number of repetitions or the RTP by performing sets to voluntary interruption or muscle failure is not necessary in initial stages of RT. In addition, it is also possible to suggest that the training volume performed by the nonfailure protocols was adequate to guarantee the occurrence of neural adaptations, which is the main physiological mechanism responsible for increased muscle strength in absence of hypertrophy. Accordingly, Nóbrega et al. (20) used muscle activation to evaluate neural adaptations, and the results demonstrated that low-load FAI and VOL protocols promote similar muscle activation during the exercising sets. It is assumed, based on electromyography data, that after a certain number of low-load repetitions, motor units cease firing and possibly recruits other motor units to maintain muscle contraction (9). In this sense, although FIX protocol had an indication to be far from the point of muscle failure, it is possible that the accumulation of sets throughout a same training session may have promoted a recruitment of higher threshold motor units. Thus, it is possible to speculate that the motor unit recruitment stimulated by low-load and lower volume protocols is sufficient to promote important strength gains in early stages of training in older adults, as previously demonstrated (12).

For RTD, no significant changes were observed after RT period. The results might be explained by the principle of specificity, once a nonspecific isometric and ballistic protocol was used to evaluate RTD, which is different of the type of contraction traditionally performed in RT protocols (i.e., dynamic contraction with moderate velocity) (28). Thus, it is possible that the RT protocols in this study were not satisfactory to induce specific neural patterns of power training (i.e., dynamic contraction with fast velocity), which could result in RTD improvements (34,37).

Age-related changes in the capacity of rising from a chair and gait speed are commonly linked to risk of falling (5,27), which directly affects the capacity of performing the activities of daily living and the quality of life (35). Previous studies demonstrated that muscle strength gains might play an important role in improving the capacity of performing functional activities (e.g., CS and HGS) (1,34). In fact, muscle strength is positively correlated to functional performance (16,19,22), what does not seem to occur between muscle hypertrophy and functional performance (30). In this sense, Reid et al. (25) showed increases for both muscle strength and functional performance after 16 weeks of low-load RT, without increments in muscle hypertrophy. Although all protocols demonstrated significant improvement for CS in this study, caution is needed to analyze such improvement in FIX protocol, once the percentage of increasing was within the CV and TE for this variable.

Regarding the other functional parameters, there were no significant changes for MGS and TUG. In agreement to our results, Van Roie et al. (24) presented no significant improvements in TUG and MGS for low-load protocols. It is possible that increases in TUG and MGS are linked to a greater capacity of acceleration and to perform rapid movements. Curiously, despite the nonsignificative improvements in the TUG test, FAI and VOL presented higher ES compared with FIX, which may indicate a slight advantage for higher volume protocols. However, it is known that older adults may present a great variability in functional responses to RT, which was noted in the results of the TUG test (−22.5% to +25.5%) (6). Thus, these results require caution and further investigation is necessary to infer about the real importance of TTV and Nrep to improve this parameter in older adults.

This study is not without limitations: (a) The relative small sample size possibly may have precluded the verification of differences between protocols, causing a type II error (33). However, this possibility was minimized through the ES analysis; (b) the lack of a direct measurement of muscle fatigue to compare the differences between protocols. However, it was attenuated by the analysis of decrease in the number of repetitions during the RT sessions; (c) the absence of dietetic control, which might have impaired our muscle hypertrophy results. However, a recent review has demonstrated that self-reported dietary habits do not largely differ between responders and nonresponders to important variables such as muscle hypertrophy (26).

In conclusion, our data suggest that in early stages of RT, even in low-load RT protocols, exercising to muscle failure is not essential to promote significant improvements in muscle strength and functional performance. In addition, progressing workload every session may not be necessary to produce significant improvements in older adults. Future studies might elucidate whether progressing the training workload throughout the training sessions is determinant to enhance the RT adaptations in longer periods of training or in trained older adults. Finally, increases in muscle mass may not be essential to induce improvements in muscle strength and functional performance in older adults in early stages of RT.

Practical Applications

Low-load RT performed to muscle failure has been commonly applied to maximize neuromuscular adaptations in different populations. However, according to our results, previously untrained older adults may similarly benefit from nonfailure low-load RT protocols (voluntary interruption or with a fixed low number of repetitions). In addition, it is not necessary that coaches promote large progressions in total training volume throughout the sessions during initial stages of training (i.e., 12 weeks) for older adults, once that neuromuscular and functional adaptations were not influenced by different total training volume progressions.

Acknowledgments

C.A. Libardi and J.G.A. Bergamasco were supported by National Council for Scientific and Technological Development (CNPq) (CAL: 302801/2018-9 and JGAB: 131539/2017-5). The authors also acknowledge all the subjects of this study. Finally, the authors declare no potential conflicts of interest.

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Keywords:

fatigue; resistance exercise; neuromuscular adaptations; physical function

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