Zourdos, Michael C.

Purpose: This study examined inter-individual response variation in muscle size and strength following training with different resistance training (RT) volumes. We hypothesized that despite clear gross variability, we would not detect clear evidence of inter-individual response variation for the primary outcomes. Additionally, we hypothesized that higher weekly set volumes would benefit muscle hypertrophy but not strength outcomes at the group-level. Methods: Sixteen recreationally trained individuals had their lower limbs randomized into either a low (LV = 8 sets per week) or high volume (HV = 16 sets per week) training condition for an initial 11-week intervention (phase 1). After a washout period, a second identical 11-week intervention (phase 2) was conducted with limbs re-randomized to the training conditions. Primary outcomes measured were vastus lateralis (VL) cross-sectional area (CSA), muscle thickness (MT), leg press one-repetition maximum (1RM), and isometric force (MVIC) at baseline, midpoint, and post-intervention for each phase. Results: Higher RT volumes benefited muscle hypertrophy (CSA = 2.04 cm2 [95% HDI: 0.11, 3.81], MT = 0.55 mm [95% HDI: -0.06, 1.19]) to a larger degree than strength outcomes (1RM = 4.05 kg [95% HDI: -1.67, 10.14], MVIC = 0.66 kg [95% HDI: -3.83, 5.07]) at the group-level. Clear gross variability was observed for all primary outcomes, but we did not detect strong evidence in support of true inter-individual response variation (CSA = 0.17 cm2 [95% HDI: 0, 3.54], MT = 0 mm [95% HDI: 0, 1.1], 1RM = 0.59 kg [95% HDI: 0, 7.92], MVIC = 4.49 kg [95% HDI: 0, 9.43]).Conclusion: Higher volumes appear to benefit muscle hypertrophy but not strength at the group-level. Additionally, we failed to detect strong evidence of interindividual response variation to different RT weekly set volumes, despite clear gross
variability.

This study examined the effect of repetitions per set as a function of changing load (percentage of one-repetition maximum) on the accuracy of intraset repetitions in reserve (RIR) predictions in the back squat and bench press. Twelve resistance trained men completed three multi-set back squat and bench press training sessions that differed in the number of target repetitions (session 1: 10 repetitions; session 2: 8 repetitions; session 3: 6 repetitions). The last set of each session was performed until muscular failure in which subjects verbally indicated when they perceived 4 RIR and 1 RIR. For each RIR prediction, RIRDIFF [perceived RIR - actual RIR] was calculated.
Differences in RIRDIFF were analyzed using both raw RIRDIFF (including positive and negative values) and absolute RIRDIFF (absolute values) via MANOVA and factorial ANOVA. The model controlled for the covariates session-type, percentage of 1RM, and total repetitions per set. Overall, RIR accuracy at the predicted 1 RIR was significantly greater (i.e., lower absolute RIRDIFF) than at the predicted 4 RIR in both the bench press (4 RIR: 1.00 ± 0.18 vs. 1 RIR: 0.69 ± 0.12; p = 0.028) and the squat (4 RIR: 1.43 ± 0.31 vs. 1 RIR: 0.79 ± 0.26; p = 0.007). No covariates significantly affected RIR accuracy (p = 0.085 – 0.518) at the predicted 1 RIR. However, at the predicted 4 RIR, the covariate repetitions per set affected raw RIRDIFF in both the squat (p = 0.007) and bench press (p < 0.001), indicating that subjects tended to overpredict RIR in lower repetition sets and underpredict RIR in higher repetition sets.

This study examined whether accuracy of intraset RIR predictions changes over time. Nine resistance trained men completed three bench press training sessions per week for six weeks, with the last set of each session performed until muscular failure. During the set to failure, subjects verbally indicated when they perceived 4 repetitions in reserve (RIR) and 1 RIR during the set. For each RIR prediction, the difference between perceived RIR and actual RIR was calculated as RIRDIFF. We analyzed differences in RIRDIFF using both the raw RIRDIFF (including positive and negative values) and the absolute values of all RIRDIFF using a factorial MANOVA. Covariates included proximity to failure of the RIR prediction, total repetitions performed per set, percentage of one-repetition maximum lifted, the week of training, and the session (1, 2, or 3 within each seek). For the raw RIRDIFF all covariates, except for percentage of 1RM (p > 0.05) were significantly related to the outcome measure at both the predicted 4 and 1 RIR (p < 0.001 to p = 0.04). Specifically, RIRDIFF was significantly higher in weeks 1-4 versus weeks 5-6 (p < 0.001 to p = 0.005). However, the only covariate which significantly impacted the absolute value RIRDIFF at both the predicted 4 (p = 0.033) and 1 RIR (p = 0.022) was total repetitions per set. These results indicate that trained men tend to shift from overpredicting to underpredicting RIR over time and that more repetitions in a set is related to more inaccurate RIR predictions. However, the actual accuracy (i.e., absolute value RIRDIFF) did not significantly change over six weeks of training.

This study examined the acute and chronic responses of brain-derived neurotrophic factor (BDNF), cathepsin B (CatB), insulin-like growth factor-1 (IGF-1), and interleukin-6 (IL-6) and if changes in these biomarkers were correlated during resistance training. Fourteen resistance trained men performed resistance training 3 days per week for 6 weeks in two groups. The only difference between groups was the proximity to failure of each set (4-6 repetitions in reserve or 1-3 repetitions in reserve). Serum was collected immediately before and after training on day 1 of weeks 1 and 6.
There were no significant group interactions for any of the biomarkers assessed, there were no main effects for time (p>0.05), and no significant correlations were observed between any of the biomarkers. However, a significant main effect for exercise for BDNF (p=0.03) and IL-6 (p=0.003) was observed. For CatB, a significant exercise × time (p=0.002) interaction was observed, indicating differences in the acute change of CatB in week 6 (+15.78%; g=0.25) vs. week 1 (-7.46%; g=0.13). In summary, these results suggest that multi-joint resistance exercise far from failure can confer a BDNF response. This investigation is the first to demonstrate the potential for acute resistance exercise to elicit a transient increase in CatB.

This study examined the longitudinal relationship between repetitions in reserve (RIR) and average concentric velocity (ACV) in the back squat and bench press exercises. Fourteen resistance-trained men were randomized into two groups (4-6RIR or 1-3RIR) and completed a six-week program. The RIR/ACV slope was significantly greater (p<0.001) in the bench press (0.027±}0.001m.s-1) than squat (0.020±}0.001m.s-1), and was steeper in 1-3RIR than 4-6RIR (p<0.001). The RIR/ACV relationship varied from set-to-set (p=0.001); however, the largest difference in ACV at the same RIR from set-to-set was only 0.044 m.s-1; likely not practically meaningful. The RIR/ACV relationship changed over time (p=0.004); however, since training was not to failure, it is unclear if this longitudinal change was due to improved RIR accuracy or a true change in the RIR/ACV relationship. Therefore, the RIR/ACV relationship is exercise-specific and practically stable from set-to-set; however, future research is needed to determine the long-term stability of this relationship.

This study examined the effect of resistance training proximity to failure on strength, muscle hypertrophy, and fatigue. Fourteen men were randomized into two groups (4-6 rating of perceived exertion-RPE per set or 7-9 RPE per set) and completed an eight-week program. Squat and bench press strength, muscle thickness, subjective fatigue, muscle soreness, and biomarkers (creatine kinase-CK and lactate dehydrogenase-LDH) were assessed. There were no significant differences (p>0.05) in the rate of strength gains and equivalence testing revealed hypertrophy was not statistically similar nor different. All results for indirect markers of muscle damage and fatigue indicated similar recovery between groups within 48 hours; however, a small between group effect size (g=0.39) existed indicating higher session RPE in the 7-9 RPE group across the entire training program. These results suggest that strength and possibly hypertrophy outcomes are similar when training each set to 4-6 RPE or 7-9 RPE in trained men.

This study examined the relationship between average concentric velocity (ACV) and repetitions in reserve (RIR) in the back squat, bench press, and deadlift. Fourteen resistance-trained men performed three experimental sessions (one for each exercise), which was comprised of 4 sets to failure at 80% of one-repetition maximum. The ACV was recorded on every repetition of every set and cross-referenced with RIR. The main findings of this study were that RIR was a significant predictor of ACV for all three exercises; the mean set ACV was significantly different between exercises (p<0.001); and the relationship between RIR and ACV was set-dependent (p<0.001). However, the within-exercise difference in ACV from set-to-set is unlikely to be practically significant as all of these ACV differences were below the threshold of 0.06 m.s-1, which is the smallest worthwhile change in ACV. Therefore, these results suggest that the RIR/ACV relationship is exercise-specific, and is stable from set-to-set.

This study examined the accuracy of predicting back squat and bench press one repetition maximum (1RM) from submaximal average concentric velocity (ACV).Seventeen resistance trained men performed a warm-up and 1RM test on the squat and bench press, in which ACV was assessed on all repetitions. The ACVs during the warmup closest to 1.0 and 0.5 m.s-1 were used in a 2-point linear regression forecast of 1RM and the ACVs established at the loads closest to 20, 50, 70, and 80% of 1RM were used in a 4-point 1RM prediction. An ANOVA indicated significant differences between predicted and actual 1RM for all predictions (p<0.001). Both Bland-Altman and Mountain plots confirmed the findings of the ANOVA as data were not tightly conformed to the respective zero difference lines. Therefore, these results suggest that a linear regression forecast using submaximal ACV does not accurately predict 1RM in the ¬back squat and bench press.

This study examined if multi-joint resistance exercises could elicit expression of biomarkers associated with neuroprotection. Thirteen well-trained males performed 4 sets to failure at 80% of a one-repetition maximum (1RM) on the back squat, bench press, and deadlift. The biomarkers measured immediately pre- and post-exercise were brain derived neurotrophic factor (BDNF), insulin-like growth factor 1 (IGF-1), cathepsin B (CatB), and interleukin 6 (IL-6). There was a main time effect (p<0.01) for BDNF with significant increases in the deadlift (p=0.01) and bench press (p=0.01) conditions, but not the squat (p=0.21). There was a main time effect (p<0.01) for IL-6 with a significant increase in the squat (p<0.01). There was no significant increase in CatB or IGF-1 (p>0.05). Additionally, there was no significant relationship between BDNF and IL-6 response.

The purpose of this research was to investigate the effects of eccentric phase
duration on concentric outcomes at 60% and 80% of one-repetition maximum (1RM) in
the squat and bench press. Sixteen resistance-trained males completed four laboratory
visits as follows: Day 1- 1RM testing; Day 2- establishment of normative eccentric
durations; Days 3 and 4- randomized fast (0.75 times) or slow (2 times) eccentric
duration variations, which were controlled by visual and auditory metronomes. Eccentric
duration was significantly and inversely correlated with average concentric velocity
(ACV) at 60% (r = 0.408) and 80% (r = -0.477) of 1RM squat and at 100% of 1RM
bench press. At 60% of 1RM squat, both fast and slow eccentric conditions produced
greater (p<0.001) peak concentric velocity (PCV) than normative duration with fast also
producing greater PCV than slow (p=0.044). Therefore, fast eccentric durations may
benefit concentric velocity.