ECSS Paris 2023: OP-BM09
INTRODUCTION: The interset rest period in resistance training is crucial in determining the total work that can be performed during a training session. When using maximal loads [>85% of one repetition maximum (1RM)], rest intervals ranging from 3 to 7 minutes are commonly recommended1,2. However, scientific evidence supporting these durations is limited although the muscular and neural mechanisms responsible for decreased performance (fatigability) can be influenced by rest duration. This study investigated the effects of rest intervals on fatigability in response to a strength training session with heavy loads. METHODS: Twenty-two resistance-trained males (mean±SD: age 23±2 years, body mass 74±7 kg, height 180±6 cm) participated in three sessions performed in a counterbalanced order. The protocol consisted of 4 sets of 3 repetitions at 90% of 1RM on a horizontal leg press machine, with rest intervals of 3 (S3), 5 (S5), or 7 min. (S7). Procedures included: isometric maximal voluntary contraction (MVC) of the lower limb, tetanic contraction of the quadriceps (50 pulses at 50 Hz), and triplets (3 pulses at 100 Hz) evoked by femoral nerve stimulation. Electromyographic (EMG) activity of the vastus lateralis (VL), and rectus femoris (RF), tissue oxygenation index (TOI) of the VL, and the rate of perceived exertion (RPE) were also measured. RESULTS: MVC force decreased more in S3 and S5 compared with S7 (p<0.001). The central activation ratio did not show any significant difference in any interset duration (p<0.05) while EMG during MVC declined in VL and RF in S3 and S5 (p<0.05), but not in S7. The tetanic force declined significantly post-session (p<0.001) with greater reductions in shorter interset intervals (34±28% S3; 22±16% S5; 21±17% S7). Triplet force decreased significantly for S3-S5 and S3-S7 (p<0.05). TOI decreased more in S3 and S5 compared with S7 (p<0.001) thus RPE increased more in S3 and S5 compared with S7 (5±1% S3; 3±1% S5; 2±1% S7, p<0.001). CONCLUSION: Our findings indicate that shorter rest intervals (S3, S5) amplify neuromuscular fatigue. The absence of central activation ratio failure suggests peripheral mechanisms as key factors in reduced performance. Accordingly, the force developed during electrically-evoked contraction decreased to a greater extent for short interset rest duration (S3 and S5). Likely due to increased metabolic stress as suggested by TOI. Additionally, higher RPE scores with shorter rests highlight increased psychophysiological strain which could reflect metabolic changes3. Overall results suggest a 7-minute interset rest as more optimal for reducing neuromuscular fatigability under high-load conditions. References: 1) Iversen, et al., Sports Med, 2021 2) Salles, et al., Sports Med, 2009 3) Allen et al., Physiol Rev, 2008
Read CV David Gamero del CastilloECSS Paris 2023: OP-BM09
INTRODUCTION: Muscle strength is an essential functional parameter during daily life activities. Muscle force typically decreases with age (Bemben et al., 1991), affecting the quality of life (Trombetti et al., 2016). Therefore, training strategies that can improve muscle strength in the elderly are of scientific and practical interest. Several training protocols in this population have been shown to improve cardiovascular function (Craighead et al., 2019), but their role in eliciting improvements in muscle force is still not completely understood. Therefore, this study aimed to compare the effects of different endurance training modalities on maximum isometric and eccentric muscle strength (torque). METHODS: Thirty-two healthy elderly participated in the study. They were divided into four work-matched training groups: moderate-intensity continuous training (concentric, 4M/4F), heavy-intensity continuous training (concentric, 4M/4F), heavy-intensity continuous training (eccentric, 4M/4F), high-intensity interval training (concentric, 4M/4F). Training modalities were carried out at the cycle ergometer (Lode for the concentric and Cyclus 2 for the eccentric modalities). The participants were tested at baseline and after 4 and 8 weeks of training. Knee extensor torque was measured using an isokinetic dynamometer (Cybex Norm); subjects were seated with the back supported and the hip joint flexed at 70°. They were requested to perform two maximal voluntary isometric contractions at a 90° knee angle and two maximal eccentric isokinetic contractions at five different angular speeds [45, 90, 150, 210, 250 °/s]. The mean torque value during the steady state of the isometric contractions and the maximum torque value during the isokinetic phase (at each angular speed) were calculated. RESULTS: The four groups were matched for age (66.5±5.2 years), stature (1.7±0.8 m) and body mass (69.2±11.2 kg). Maximum eccentric torque was unaffected by training modality in all groups. Maximum isometric (concentric) torque increased from 130.7±70.8 Nm to 142.3±78.7 Nm (p=0.041) in the high-intensity continuous training group after 4 weeks of training; no further improvements were observed after 8 weeks. No significant differences were observed (either after 4 or 8 weeks) in the other training groups in concentric torque. CONCLUSION: Our data indicate that these training protocols have trivial or no effect on maximum isometric and eccentric torque in an elderly population. Only in the high-intensity continuous training group did torque significantly improve after 4 weeks, indicating a positive impact of training intensity on muscle force capacity. The eccentric training protocol did not affect eccentric torque. Although endurance training improves cardiovascular function in older adults (Craighead et al., 2019), this is not the case for muscle force.
Read CV Trinchi MicheleECSS Paris 2023: OP-BM09
INTRODUCTION: Quantifying lower body muscle volume (VOL) with magnetic resonance (MR) imaging requires segmentation of a relatively large number of axial images along the length of the muscle (1). In contrast, maximum anatomical cross-sectional area (ACSAmax), can be derived more efficiently as only a small number of images around ACSAmax need to be segmented. Currently the extent to which changes in ACSAmax across individual muscles of the lower body are associated with changes in VOL following resistance training (RT) has received little attention, with prior work only focusing on the relationship between RT-induced changes ACSAmax and VOL for the overall quadriceps femoris (QF; 2). The purpose of this study was to determine the relationship between RT-induced changes in ACSAmax and changes in VOL across individual muscles of the QF, hamstrings (HAMS), and also the gluteus maximus (Gmax). METHODS: Thirty-nine healthy young men participated in the study. Before and after 15 wk of lower body RT (knee extension, knee flexion, leg press; x3/wk) dominant limb axial MR images between the anterior superior iliac spine and lateral tibial condyle were acquired. Scans were segmented to quantify ACSAmax and VOL of the Gmax, the constituent muscles of the QF and HAMS. Pearson’s product moment bivariate correlations were performed between pre to post RT percentage changes in ACSAmax and VOL for each muscle/muscle group. RESULTS: Percentage changes in ACSAmax and VOL following RT were correlated for the overall QF (r=0.874, p<0.001) and HAMS (r=0.966, p<0.001) muscle groups as well as all individual muscles (vastus lateralis r= 0.699, vastus intermedius r= 0.646, vastus medialis r= 0.894, rectus femoris r= 0.897, biceps femoris short head r= 0.923, biceps femoris long head r= 0.880, semitendinosus r= 0.834, semimembranosus r=0.890, Gmax r= 0.820, [all] p<0.001). CONCLUSION: Overall RT-induced changes in QF (76%) and HAMS (93%) ACSAmax explained moderate to high amounts of variance in corresponding changes in VOL. Following RT, the extent that percentage changes in ACSAmax explained variance in changes in VOL across individual muscles differed markedly (42% vastus intermedius to 85% biceps femoris short head). In conclusion, the extent to which RT-induced changes in ACSAmax are related to changes in VOL varied notably across key individual lower body muscles and should not uniformly be accepted as a substitute for or alternative to directly assessing changes in muscle volume. REFERENCES: 1. Balshaw et al. 2023. Acta Physiol. 237(2); e13903 2. Tracy et al. 2003. Med Sci Sports Exerc. 35(3); 425–433
Read CV Tom BalshawECSS Paris 2023: OP-BM09