Towards an improved understanding of proximity-to-failure in resistance training and its influence on skeletal muscle hypertrophy, neuromuscular fatigue, muscle damage, and perceived discomfort: A scoping review

Exploring the Dose-Response Relationship Between Estimated Resistance Training Proximity to Failure, Strength Gain, and Muscle Hypertrophy: A Series of Meta-Regressions

BACKGROUND

The proximity to failure in which sets are terminated has gained attention in the scientific literature as a potentially key resistance training variable. Multiple meta-analyses have directly (i.e., failure versus not to failure) or indirectly (e.g., velocity loss, alternative set structures) evaluated the effect of proximity to failure on strength and muscle hypertrophy outcomes categorically; however, the dose-response effects of proximity to failure have not been analyzed collectively in a continuous manner.

OBJECTIVE

To meta-analyze the aforementioned areas of relevant research, proximity to failure was quantified as the number of repetitions in reserve (RIR). Importantly, the RIR associated with each effect in the analysis was estimated on the basis of the available descriptions of the training interventions in each study. Data were extracted and a series of exploratory multilevel meta-regressions were performed for outcomes related to both strength and muscle hypertrophy. A range of sensitivity analyses were also performed. All models were adjusted for the effects of load, method of volume equating, duration of intervention, and training status.

RESULTS

The best fit models for both strength and muscle hypertrophy outcomes demonstrated modest quality of overall fit. In all of the best-fit models for strength, the confidence intervals of the marginal slopes for estimated RIR contained a null point estimate, indicating a negligible relationship with strength gains. However, in all of the best-fit models for muscle hypertrophy, the marginal slopes for estimated RIR were negative and their confidence intervals did not contain a null point estimate, indicating that changes in muscle size increased as sets were terminated closer to failure.

CONCLUSIONS

The dose-response relationship between proximity to failure and strength gain appears to differ from the relationship with muscle hypertrophy, with only the latter being meaningfully influenced by RIR. Strength gains were similar across a wide range of RIR, while muscle hypertrophy improves as sets are terminated closer to failure. Considering the RIR estimation procedures used, however, the exact relationship between RIR and muscle hypertrophy and strength remains unclear. Researchers and practitioners should be aware that optimal proximity to failure may differ between strength and muscle hypertrophy outcomes, but caution is warranted when interpreting the present analysis due to its exploratory nature. Future studies deliberately designed to explore the continuous nature of the dose-response effects of proximity to failure in large samples should be considered.

The Autoregulation Rest-Redistribution Training Method Mitigates Sex Differences in Neuromuscular and Perceived Fatigue During Resistance Training

PURPOSE

To examine the sex differences in performance and perceived fatigue during resistance training prescribed using traditional (TRA) and autoregulation rest-redistribution training (ARRT) approaches.

METHODS

Twelve resistance-trained men and 12 women completed 2 sessions including the bench-press exercise matched for load (75% of 1-repetition maximum), volume (24 repetitions), and total rest (240 s). Sessions were performed in a counterbalanced randomized design with TRA consisting of 3 sets of 8 repetitions with 120-second interset rest and ARRT employing a personalized combination of clusters, repetitions per cluster, and between-clusters rest regulated with a 20% velocity-loss threshold. The effects of TRA and ARRT on velocity loss, unilateral isometric peak force, and rating of fatigue (ROF) were compared between sexes.

RESULTS

The velocity loss was generally lower during ARRT compared with TRA (-0.47% [0.11%]), with velocity loss being mitigated by ARRT to a greater extent among males compared with females (-0.37% [0.15%]). A smaller unilateral isometric peak force decline was observed after ARRT than TRA among males compared with females (-38.4 [8.4] N). Lower ROF after ARRT than TRA was found among males compared to females (-1.97 [0.55] AU). Additionally, males reported greater ROF than females across both conditions (1.92 [0.53] AU), and ARRT resulted in lower ROF than TRA overall (-0.83 [0.39] AU).

CONCLUSIONS

The ARRT approach resulted in decreased velocity loss, peak force impairment, and ROF compared with TRA in both sexes. However, male subjects exhibited more pronounced acute within-session benefits from the ARRT method.

Does Fatigue Affect the Perception of Velocity Accuracy During Resistance Training?

ABSTRACT

Romagnoli, R and Piacentini, MF. Does fatigue affect the perception of velocity accuracy during resistance training? J Strength Cond Res 38(7): 1243-1247, 2024-The purpose of this study was to investigate whether perception of barbell velocity (PV) is affected by fatigue induced by 2 different training protocols. Twenty-two subjects were randomly divided into 2 groups: 10% velocity loss group (VL10) and repetitions to failure group (EX). Both protocols included 5 sets at 75% 1 repetition maximum but differed in the number of repetitions performed (Reps). Perception of barbell velocity was assessed in the back squat exercise during a test with 3 blinded loads (heavy, medium, light) 1 day rested (REST) and 1 day immediately following 1 of the 2 designated training protocols (POST). The accuracy of the PV was analyzed by calculating the delta score (ds), that is, the difference between perceived velocity (Vp) and real velocity of the barbell (Vr). During training, each group performed significantly different Reps per set (VL10: 3.9 ± 1.4; EX: 13.8 ± 6.3, p < 0.001) and consequently reported different levels of perceived exertion and repetitions in reserve ( p < 0.001). Real velocity and ds did not change between REST and POST-VL10 conditions at all loads. Although a significant decrease in Vr was found at light and medium loads ( p < 0.05) between REST and POST in the EX-Group, no significant differences were detected in the ds. These results demonstrate that Vp is a stable parameter on which practitioners can base their training despite different levels of fatigue.

Sex and Equipment Impact on Lifting Velocity and the Maximum Repetitions in Bench Press

This study investigated how equipment and sex affect the prediction accuracy of the maximum number of repetitions performed to failure (RTF) using the fastest mean velocity of the set (MVfastest). Sixteen men and twelve women completed four sessions (two using free-weight equipment and two sessions using the Smith machine). Each session involved three sets of repetitions to failure against the 65%, 75%, and 85% of the one-repetition maximum, interspersed by 10-min of rest. The goodness-of-fit of the individualized RTF-MVfastest relationships was comparable between both equipment types and sexes (P≥0.510). Moreover, there were not significant differences in the MVfastest associated with RTF between equipment types (P≥0.258). However, the MVfastest associated with RTF was higher for men than for women in repetitions 6 to 15 (P≤0.043; ES≥0.69). In addition, the absolute errors when predicting RTF showed no significant differences between equipment types and loads (P<0.444). Specifically, these RTF estimates were within an acceptable range for men (<2 repetitions), but not for women (≥2 repetitions) (main effect of sex: P≤0.018; ES≥0.58). These findings suggest that individualized RTF-MVfastest equations estimate the RTF with an acceptable precision in men during bench press exercises in both equipment types but exhibit lower precision for women.

Resistance Exercise Minimal Dose Strategies for Increasing Muscle Strength in the General Population: an Overview

Many individuals do not participate in resistance exercise, with perceived lack of time being a key barrier. Minimal dose strategies, which generally reduce weekly exercise volumes to less than recommended guidelines, might improve muscle strength with minimal time investment. However, minimal dose strategies and their effects on muscle strength are still unclear. Here our aims are to define and characterize minimal dose resistance exercise strategies and summarize their effects on muscle strength in individuals who are not currently engaged in resistance exercise. The minimal dose strategies overviewed were: "Weekend Warrior," single-set resistance exercise, resistance exercise "snacking," practicing the strength test, and eccentric minimal doses. "Weekend Warrior," which minimizes training frequency, is resistance exercise performed in one weekly session. Single-set resistance exercise, which minimizes set number and session duration, is one set of multiple exercises performed multiple times per week. "Snacks," which minimize exercise number and session duration, are brief bouts (few minutes) of resistance exercise performed once or more daily. Practicing the strength test, which minimizes repetition number and session duration, is one maximal repetition performed in one or more sets, multiple days per week. Eccentric minimal doses, which eliminate or minimize concentric phase muscle actions, are low weekly volumes of submaximal or maximal eccentric-only repetitions. All approaches increase muscle strength, and some approaches improve other outcomes of health and fitness. "Weekend Warrior" and single-set resistance exercise are the approaches most strongly supported by current research, while snacking and eccentric minimal doses are emerging concepts with promising results. Public health programs can promote small volumes of resistance exercise as being better for muscle strength than no resistance exercise at all.

Accuracy of Intraset Repetitions-in-Reserve Predictions During the Bench Press Exercise in Resistance-Trained Male and Female Subjects

ABSTRACT

Refalo, MC, Remmert, JF, Pelland, JC, Robinson, ZP, Zourdos, MC, Hamilton, DL, Fyfe, JJ, and Helms, ER. Accuracy of intraset repetitions-in-reserve predictions during the bench press exercise in resistance-trained male and female subjects. J Strength Cond Res 38(3): e78-e85, 2024-This study assessed the accuracy of intraset repetitions-in-reserve (RIR) predictions to provide evidence for the efficacy of RIR prescription as a set termination method to inform proximity to failure during resistance training (RT). Twenty-four resistance trained male ( n = 12) and female ( n = 12) subjects completed 2 experimental sessions involving 2 sets performed to momentary muscular failure (barbell bench press exercise) with 75% of 1 repetition maximum (1RM), whereby subjects verbally indicated when they perceived to had reached either 1 RIR or 3 RIR. The difference between the predicted RIR and the actual RIR was defined as the "RIR accuracy" and was quantified as both raw (i.e., direction of error) and absolute (i.e., magnitude of error) values. High raw and absolute mean RIR accuracy (-0.17 ± 1.00 and 0.65 ± 0.78 repetitions, respectively) for 1-RIR and 3-RIR predictions were observed (including all sets and sessions completed). We identified statistical equivalence (equivalence range of ±1 repetition, thus no level of statistical significance was set) in raw and absolute RIR accuracy between (a) 1-RIR and 3-RIR predictions, (b) set 1 and set 2, and (c) session 1 and session 2. No evidence of a relationship was found between RIR accuracy and biological sex, years of RT experience, or relative bench press strength. Overall, resistance-trained individuals are capable of high absolute RIR accuracy when predicting 1 and 3 RIR on the barbell bench press exercise, with a minor tendency for underprediction. Thus, RIR prescriptions may be used in research and practice to inform the proximity to failure achieved upon set termination.

The Connection Between Resistance Training, Climbing Performance, and Injury Prevention

BACKGROUND

Climbing is an intricate sport composed of various disciplines, holds, styles, distances between holds, and levels of difficulty. In highly skilled climbers the potential for further strength-specific adaptations to increase performance may be marginal in elite climbers. With an eye on the upcoming 2024 Paris Olympics, more climbers are trying to maximize performance and improve training strategies. The relationships between muscular strength and climbing performance, as well as the role of strength in injury prevention, remain to be fully elucidated. This narrative review seeks to discuss the current literature regarding the effect of resistance training in improving maximal strength, muscle hypertrophy, muscular power, and local muscular endurance on climbing performance, and as a strategy to prevent injuries.

MAIN BODY

Since sport climbing requires exerting forces against gravity to maintain grip and move the body along the route, it is generally accepted that a climber`s absolute and relative muscular strength are important for climbing performance. Performance characteristics of forearm flexor muscles (hang-time on ledge, force output, rate of force development, and oxidative capacity) discriminate between climbing performance level, climbing styles, and between climbers and non-climbers. Strength of the hand and wrist flexors, shoulders and upper limbs has gained much attention in the scientific literature, and it has been suggested that both general and specific strength training should be part of a climber`s training program. Furthermore, the ability to generate sub-maximal force in different work-rest ratios has proved useful, in examining finger flexor endurance capacity while trying to mimic real-world climbing demands. Importantly, fingers and shoulders are the most frequent injury locations in climbing. Due to the high mechanical stress and load on the finger flexors, fingerboard and campus board training should be limited in lower-graded climbers. Coaches should address, acknowledge, and screen for amenorrhea and disordered eating in climbers.

CONCLUSION

Structured low-volume high-resistance training, twice per week hanging from small ledges or a fingerboard, is a feasible approach for climbers. The current injury prevention training aims to increase the level of performance through building tolerance to performance-relevant load exposure and promoting this approach in the climbing field.

Peak Week Carbohydrate Manipulation Practices in Physique Athletes: A Narrative Review

BACKGROUND

Physique athletes are ranked by a panel of judges against the judging criteria of the corresponding division. To enhance on-stage presentation and performance, competitors in certain categories (i.e. bodybuilding and classic physique) achieve extreme muscle size and definition aided by implementing acute "peaking protocols" in the days before competition. Such practices can involve manipulating nutrition and training variables to increase intramuscular glycogen and water while minimising the thickness of the subcutaneous layer. Carbohydrate manipulation is a prevalent strategy utilised to plausibly induce muscle glycogen supercompensation and subsequently increase muscle size. The relationship between carbohydrate intake and muscle glycogen saturation was first examined in endurance event performance and similar strategies have been adopted by physique athletes despite the distinct physiological dissimilarities and aims between the sports.

OBJECTIVES

The aim of this narrative review is to (1) critically examine and appraise the existing scientific literature relating to carbohydrate manipulation practices in physique athletes prior to competition; (2) identify research gaps and provide direction for future studies; and (3) provide broad practical applications based on the findings and physiological reasoning for coaches and competitors.

FINDINGS

The findings of this review indicate that carbohydrate manipulation practices are prevalent amongst physique athletes despite a paucity of experimental evidence demonstrating the efficacy of such strategies on physique performance. Competitors have also been observed to manipulate water and electrolytes in conjunction with carbohydrate predicated on speculative physiological mechanisms which may be detrimental for performance.

CONCLUSIONS

Further experimental evidence which closely replicates the nutritional and training practices of physique athletes during peak week is required to make conclusions on the efficacy of carbohydrate manipulation strategies. Quasi-experimental designs may be a feasible alternative to randomised controlled trials to examine such strategies due to the difficulty in recruiting the population of interest. Finally, we recommend that coaches and competitors manipulate as few variables as possible, and experiment with different magnitudes of carbohydrate loads in advance of competition if implementing a peaking strategy.

Similar muscle hypertrophy following eight weeks of resistance training to momentary muscular failure or with repetitions-in-reserve in resistance-trained individuals

This study examined the influence of resistance training (RT) proximity-to-failure, determined by repetitions-in-reserve (RIR), on quadriceps hypertrophy and neuromuscular fatigue. Resistance-trained males (n = 12) and females (n = 6) completed an 8-week intervention involving two RT sessions per week. Lower limbs were randomised to perform the leg press and leg extension exercises either to i) momentary muscular failure (FAIL), or ii) a perceived 2-RIR and 1-RIR, respectively (RIR). Muscle thickness of the quadriceps [rectus femoris (RF) and vastus lateralis (VL)] and acute neuromuscular fatigue (i.e., repetition and lifting velocity loss) were assessed. Data was analysed with Bayesian linear mixed-effect models. Increases in quadriceps thickness (average of RF and VL) from pre- to post-intervention were similar for FAIL [0.181 cm (HDI: 0.119 to 0.243)] and RIR [0.182 cm (HDI: 0.115 to 0.247)]. Between-protocol differences in RF thickness slightly favoured RIR [-0.036 cm (HDI: -0.113 to 0.047)], but VL thickness slightly favoured FAIL [0.033 cm (HDI: -0.046 to 0.116)]. Mean volume was similar across the RT intervention between FAIL and RIR. Lifting velocity and repetition loss were consistently greater for FAIL versus RIR, with the magnitude of difference influenced by the exercise and the stage of the RT intervention.

Influence of Resistance Training Proximity-to-Failure on Skeletal Muscle Hypertrophy: A Systematic Review with Meta-analysis

BACKGROUND AND OBJECTIVE

This systematic review with meta-analysis investigated the influence of resistance training proximity-to-failure on muscle hypertrophy.

METHODS

Literature searches in the PubMed, SCOPUS and SPORTDiscus databases identified a total of 15 studies that measured muscle hypertrophy (in healthy adults of any age and resistance training experience) and compared resistance training performed to: (A) momentary muscular failure versus non-failure; (B) set failure (defined as anything other than momentary muscular failure) versus non-failure; or (C) different velocity loss thresholds.

RESULTS

There was a trivial advantage for resistance training performed to set failure versus non-failure for muscle hypertrophy in studies applying any definition of set failure [effect size=0.19 (95% confidence interval 0.00, 0.37), p=0.045], with no moderating effect of volume load (p=0.884) or relative load (p=0.525). Given the variability in set failure definitions applied across studies, sub-group analyses were conducted and found no advantage for either resistance training performed to momentary muscular failure versus non-failure for muscle hypertrophy [effect size=0.12 (95% confidence interval -0.13, 0.37), p=0.343], or for resistance training performed to high (>25%) versus moderate (20-25%) velocity loss thresholds [effect size=0.08 (95% confidence interval -0.16, 0.32), p=0.529].

CONCLUSION

Overall, our main findings suggest that (i) there is no evidence to support that resistance training performed to momentary muscular failure is superior to non-failure resistance training for muscle hypertrophy and (ii) higher velocity loss thresholds, and theoretically closer proximities-to-failure do not always elicit greater muscle hypertrophy. As such, these results provide evidence for a potential non-linear relationship between proximity-to-failure and muscle hypertrophy.

Influence of Resistance Training Proximity-to-Failure, Determined by Repetitions-in-Reserve, on Neuromuscular Fatigue in Resistance-Trained Males and Females

BACKGROUND

This study examined the influence of proximity-to-failure in resistance training (RT), using subjective repetitions-in-reserve (RIR) prediction, on neuromuscular fatigue and perceptual responses.

METHODS

Twenty-four resistance-trained males (n = 12) and females (n = 12) completed three experimental trials in a randomised order, each involving six RT sets (barbell bench press) with 75% 1-RM performed to either momentary muscular failure (FAIL), 1-RIR, or 3-RIR. Changes in lifting velocity with a fixed load were assessed from pre-exercise to post-exercise with the aim of quantifying acute neuromuscular fatigue (4 min post-exercise) and the associated time course of recovery (24 and 48 h post-exercise), and from the first to final set performed. Perceptual responses to RT were assessed at multiple time points during and following RT.

RESULTS

Decreases in lifting velocity at 4 min post-exercise were greater for FAIL ( - 25%) versus 1-RIR ( - 13%) and 3-RIR ( - 8%), with greater decreases for male ( - 29%) versus female ( - 21%) participants following FAIL. At 24 h post-exercise, decreases in lifting velocity were greater for FAIL ( - 3%) and 1-RIR ( - 3%) versus 3-RIR (+ 2%), with all between-protocol differences diminishing at 48 h post-exercise. Loss of lifting velocity from the first to final set was greater for FAIL ( - 22%) versus 1-RIR ( - 9%) and 3-RIR ( - 6%), with a greater lifting velocity loss from the first to final set for males ( - 15%) versus females ( - 9%). As proximity-to-failure neared, ratings of perceived discomfort, exertion, and muscle soreness increased, general feelings worsened, and perceived recovery decreased.

CONCLUSION

These findings support a linear relationship between RT proximity-to-failure and both acute neuromuscular fatigue and negative perceptual responses, which may influence long-term physiological adaptations and adherence to RT.

Resistance training volume does not influence lean mass preservation during energy restriction in trained males

This study investigated the effects of a relatively high- versus moderate-volume resistance training program on changes in lean mass during caloric restriction. Thirty-eight resistance-trained males were randomized to perform either a high-volume (HVG; 5 sets/exercise) or a moderate-volume (MVG; 3 sets/exercise) resistance training program. Both groups were supervised during lower body training. Participants consumed 30 kcal/kg for 6 weeks after 1 week of weight maintenance (45 kcal/kg), with protein intake fixed at 2.8 g/kg fat-free mass. Muscle thickness of the m. rectus femoris, body composition, contractile properties, stiffness, mood, and sleep status were assessed at pre-, mid-, and post-study. No significant group × time interaction was observed for muscle thickness of the m. rectus femoris at 50% (∆ [post-pre] 0.36 ± 0.93 mm vs. ∆ -0.01 ± 1.59 mm; p = 0.226) and 75% length (∆ -0.32 ± 1.12 mm vs. ∆ 0.08 ± 1.14 mm; p = 0.151), contractility, sleep, and mood in the HVG and MVG, respectively. Body mass (HVG: ∆ -1.69 ± 1.12 kg vs. MVG: ∆ -1.76 ± 1.76 kg) and lean mass (∆ -0.51 ± 2.30 kg vs. ∆ -0.92 ± 1.59 kg) decreased significantly in both groups (p = 0.022), with no between-group difference detected (p = 0.966). High-volume resistance training appears to have neither an advantage nor disadvantage over moderate-volume resistance training in terms of maintaining lean mass or muscle thickness. Given that both groups increased volume load and maintained muscle contractility, sleep quality, and mood, either moderate or higher training volumes conceivably can be employed by resistance-trained individuals to preserve muscle during periods of moderate caloric restriction.