Acute neuromuscular and hormonal responses to 20 versus 40% velocity loss in males and females before and after 8 weeks of velocity-loss resistance training

This is a self-archived version of an original article. This version may differ from the original in pagination and typographic details. Author(s): Title: Year: Version: Copyright: Rights: Rights url: Please cite the original version: CC BY-NC 4.0 https://creativecommons.org/licenses/by-nc/4.0/ Acute neuromuscular and hormonal responses to 20 versus 40% velocity loss in males and females before and after 8 weeks of velocity-loss resistance training © 2022 The Authors. Experimental Physiology published by John Wiley & Sons Ltd on behalf of The Physiological Society. Published version Walker, Simon; Häkkinen, Keijo; Virtanen, Roosa; Mane, Shashank; Bachero‐ Mena, Beatriz; Pareja‐Blanco, Fernando Walker, S., Häkkinen, K., Virtanen, R., Mane, S., Bachero‐Mena, B., & Pareja‐Blanco, F. (2022). Acute neuromuscular and hormonal responses to 20 versus 40% velocity loss in males and females before and after 8 weeks of velocity-loss resistance training. Experimental Physiology, 107(9), 1046-1060. https://doi.org/10.1113/EP090371 2022 Received: 12 February 2022 Accepted: 29 July 2022 DOI: 10.1113/EP090371 RESEARCH ARTICLE Acute neuromuscular and hormonal responses to 20 versus 40% velocity loss in males and females before and after 8 weeks of velocity-loss resistance training Simon Walker1Keijo Häkkinen1Roosa Virtanen1Shashank Mane1 Beatriz Bachero-Mena2Fernando Pareja-Blanco3 1NeuroMuscular Research Center, Faculty of Sport and Health Sciences, University of Jyväskylä, Jyväskylä, Finland 2Department of Human Movement and Sports Performance, University of Seville, Seville, Spain 3Physical Performance and Sports Research Center, Department of Sports and Computer Sciences, Universidad Pablo de Olavide, Seville, Spain Correspondence Simon Walker, Room VIV225, NeuroMuscular Research Center, Faculty of Sport and Health Sciences, University of Jyväskylä, Jyväskylä, FI-40014, Finland. Email: simon.[email protected] Funding information None Handling Editor: Colleen Deane Abstract Scientific examination of velocity-based resistance training (VBRT) has increased recently, but how males and females respond to different VBRT protocols or how these acute responses are modified after a period of training is unknown. Habitually resistance-trained males and females followed either a 20 or 40% velocity-loss programme for 8 weeks. Acute squat loading tests (five sets, 70% one-repetition maximum load, 3 min rest) were performed before and after the training period. Tests of maximum neuromuscular performance and blood sampling were conducted before, within 10 min of completion (POST) and 24 h after each acute loading test. Testing included countermovement jump, resting femoral nerve electrical stimulation and bilateral isometric leg press. Blood samples were analysed for whole-blood lactate, serum testosterone, cortisol, growth hormone and creatine kinase concentrations. Countermovement jump height, maximum isometric bilateral leg-press force and the force from a 10 Hz doublet decreased in all groups at POST after 20 and 40% velocity loss. Only males showed reduced force from the 100 Hz doublet and voluntary force over 100 ms at POST before training. The 40% velocity loss led to increased blood lactate and growth hormone responses before training in both males and females. After training, more systematic and equivalent responses in force over 100 ms, force from a 100 Hz doublet and blood lactate were observed regardless of sex/VBRT protocol. Overall, acute responses were greater from 40% VBRT, and males were more susceptible to acute loss in force production capacity before the training period. These VBRT protocoland sex-related differences were diminished after training. KEYWORDS electrical stimulation, fatigue, low frequency, power, sex, strength This is an open access article under the terms of the Creative Commons Attribution-NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes. © 2022 The Authors. Experimental Physiology published by John Wiley & Sons Ltd on behalf of The Physiological Society. 1046 wileyonlinelibrary.com/journal/eph Experimental Physiology. 2022;107:1046–1060. WALKER ET AL.1047 1INTRODUCTION Fatigability, the magnitude of acute reduction in force production capacity, owing to isometric muscular contraction is typically lower in females compared with males (Petrofsky & Lind, 1975; Yoon et al., 2007). Some authors have suggested that prolonged time to task failure during submaximal isometric contractions are attributable to differing muscle perfusion (Yoon et al., 2007), potentially owing to greater intramuscular pressure in males, which is evoked by higher absolute force levels. Indeed, this phenomenon is not observed when the sexes are matched for strength (Hunter et al., 2004). Furthermore, recent evidence suggests that sex differences in fatiguability are more likely to be attributable to the greater proportion of type I muscle fibres and slower muscle oxygen desaturation in females (Hunter et al., 2009; Keller & Kennedy, 2021; Wüst et al., 2008). Between-sex investigations of fatiguability using dynamic contractions are scarce in comparison to studies on isometric contractions. Nevertheless, it appears that a slow lifting tempo leads to similar observations of fatigue resistance in females (Häkkinen, 1994; Yoon et al., 2015) to those observed from isometric contractions. One area of current contention is when external loads are lifted with maximal velocity. Linnamo et al. (1998) observed that 5 ×10 × 40% one-repetition maximum (1-RM) leg-press power loading led to lower reductions in maximal and rapid force production in females (approximately −10%) compared with males (approximately −25%). Single-joint knee-extensor loadings resulted in a decreased maximal torque of ∼18% in males and ∼10% in females immediately after 3 × 30 ×20% maximum isometric torque contractions every 3 s (Senefeld et al., 2013). In contrast, elbow flexion contractions in the study by Senefeld et al. (2013) led to similar decreases in maximal isometric torque between sexes (approximately −15% in males vs. −13% in females), potentially suggesting muscle-specific influencing factors. Nevertheless, as discussed in the preceding text, it is justifiable to confirm potential between-sex fatigability after fast contractions and to investigate the acute responses to electrical stimulation in males and females. From a practical perspective, using generic training protocols (i.e., a number of sets and repetitions for a given percentage of maximum strength) might inherently increase heterogeneity in the acute responses, considering that a different number of repetitions per set with the same relative load can be performed by different individuals (González-Badillo et al., 2017). Following the predictability of a strongly correlated load–velocity relationship, both the intensity and the volume of loading can be programmed using velocity-based resistance training (VBRT). At present, no study has investigated potential between-sex fatigability when intra-set velocity loss is standardized in males and females. It would be reasonable to hypothesize that the previously observed fatigue resistance in females would be diminished when sets are continued until a predetermined fatigue level. Fatigue, fatigability and the intensity and volume are intrinsically interlinked and result in varying metabolic stress and acute endocrine responses to loading. Acute resistance loadings with higher New Findings ∙What is the central question of this study? Do males and females differ in fatiguability during dynamic loadings, and what are the acute neuromuscular and hormonal responses to 20 versus 40% velocity-loss resistance loadings? How does an 8-week velocity-loss resistance training period modify acute neuromuscular and hormonal responses in males and females? ∙What is the main finding and its importance? Using resistance training methods that regulated the within-set fatigue limit, males appeared to be more susceptible to fatigue than females before the training period. This between-sex difference was diminished after training. The predominant mechanisms of fatigue from 20 and 40% velocitybased resistance training appear to be within the musculature. intensity and volume lead to greater acute increases in blood lactate concentration (Häkkinen & Pakarinen, 1993; Kraemer et al., 1990). This greater metabolic stress is accompanied by larger increases in serum hormone concentrations of testosterone, growth hormone and cortisol (Häkkinen & Pakarinen, 1993; Kraemer et al., 1990; Smilios et al., 2003). In particular, associations between loading-induced increases in blood lactate and serum growth hormone have been observed (Gordonetal.,1994; Häkkinen & Pakarinen, 1993). It would be logical to expect, therefore, that greater acute responses would occur from velocity-loss protocols where greater fatigue occurs from a higher number of repetitions performed per set (e.g., 40 versus 20%), regardless of sex. To date, no data exist on the acute neuromuscular and hormonal responses to different VBRT methods despite the current popularity of the topic, and again, potential sex-related differences have not been studied using standardized velocity-loss protocols to our knowledge. Such investigation is justified, because females have previously demonstrated blunted acute growth hormone responses after power loading, at least using generic protocols (Linnamo et al., 2005). Finally, given that work from our laboratory has repeatedly shown that fatiguability differs after several weeks of resistance training (Ahtiainen et al., 2003; Walker et al., 2013, 2017,2015), it is also pertinent to assess acute responses before versus after a short-term training programme. Therefore, the purpose of the present study was to investigate acute neuromuscular and hormonal responses to two different velocity-loss protocols (20 and 40% velocity loss) before and after an 8-week resistance training period using the corresponding 1048 WALKER ET AL. 24 men age 26 ± 4 years 23 women age 26 ± 3 years M20%VL (n=12) M20%VL (n=11) Drop out (n=1) Drop out (n=2) Drop out (n=3) Drop out (n=4) M40%VL (n=12) M40%VL (n=10) F20%VL (n=12) F20%VL (n=9) F40%VL (n=11) F40%VL (n=7) Postintervention tests Acute loading test 2 Acute loading test 1 Baseline tests Control tests 8-week training intervention Week -2 -1 0 9 10 8-week training intervention FIGURE 1 Study flow and time line. Outcome measures from the training intervention have been reported previously (Rissanen et al., 2022). Dropouts were attributable to illness (n=2), injury related to the study methods (n=2), injury not related to the study methods (n=1), lack of motivation/interest to continue (n=2) and undisclosed pregnancy (n=1). Two females were also removed from 40%VL analyses owing to atypical hormone concentrations, potentially attributable to their contraceptive medication. The final sample size for each group taken into analyses can be seen in the boxes at the top right corner. Abbreviations: M20%VL, males training to 20% velocity loss per set; M40%VL, males training to 40% velocity loss per set; F20%VL, females training to 20% velocity loss per set; F40%VL, females training to 40% velocity loss per set velocity-loss threshold in habitually resistance-trained males and females. 2METHODS 2.1 Ethical approval The study was conducted according to the Declaration of Helsinki (2013), except for registration in a database, and was granted ethical clearance by the Ethical Committee of the University of Jyväskylä (23/05/17). Written informed consent was obtained from the subjects before measurements. 2.2 Study design This was a sub-study of a larger 8-week training-intervention study that we conducted from August 2017 to December 2017, and the outcome measures from the training intervention (prevs. posttraining) have been reported previously (Rissanen et al., 2022). Figure 1shows the study design and time line. Subjects were divided by sex, then males and females were pair matched based on 1-RM performance obtained during the control test. Variance between pairs was 0.3 ±4.5% for males and 6.2 ±3.6% for females. Members of each pair were then randomized to either a 20% velocity-loss group (20%VL) or a 40% velocity-loss group (40%VL), with the exception of one woman who did not have a pair and was randomized to 20%VL. During training (two sessions per week) and the acute loading tests, subjects performed concentric repetitions as fast as possible during each set until the mean propulsive velocity (MPV) reached the assigned level for that group (i.e., 20% loss for 20%VL and 40% loss for 40%VL). At this point, the set was terminated and the 3 min allocated inter-set rest period was initiated. Acute loading tests were scheduled throughout the day (range 09.00–20.00 h), but the test time for each subject was standardized (±1 h), and this time was closely matched to their training time throughout the study. Measurements of neuromuscular function and blood samples were taken before the loading protocol (PRE), within 10 min of completing the loading protocol (POST) and 24 h after the completion of the loading protocol (POST24). The order of the measurements before and 24 h after the loading was as follows: (1) fingertip and venous blood sampling; (2) countermovement jump trials; (3) passive electrical stimulation tests; (4) maximal unilateral isometric knee extension with superimposed electrical stimulation trials; (5) maximal bilateral isometric leg-press trials; and (6) maximal concentric velocity trials with a load of 60% 1-RM. The order of the measurements immediately after the loading was as follows: (1) countermovement jump; (2) fingertip blood sampling; (3) passive electrical stimulation; (4) maximal unilateral isometric knee extension with superimposed electrical stimulation; (5) maximal bilateral WALKER ET AL.1049 TABLE 1 Subject characteristics at baseline Characteristic M20%VL (n=11) M40%VL (n=10) F20%VL (n=9) F40%VL (n=7) Age (years) 26.5 ±4.6 26.3 ±3.3 25.8 ±3.0 25.9 ±3.3 Height (cm) 178.8 ±6.2 181.2 ±6.0 166.6 ±6.2 165.6 ±8.0 Body mass (kg) 82.3 ±14.3 81.5 ±8.0 61.8 ±4.3 60.5 ±9.3 Fat (%) 16.0 ±6.8 14.2 ±4.2 21.1 ±4.6 22.1 ±7.1 Squat 1-RM (kg) 113.7 ±28.0 109.1 ±15.8 66.3 ±13.1 63.9 ±14.4 Abbreviations: M20%VL, males training to 20% velocity loss per set; M40%VL, males training to 40% velocity loss per set; F20%VL, females training to 20% velocity loss per set; F40%VL, females training to 40% velocity loss per set; 1-RM, one-repetition maximum. isometric leg press; (6) maximal concentric velocity trials with a load of 60% 1-RM; and (7) fingertip and venous blood sampling. Exact timings of these measurements are described in detail in subsection 2.5. 2.3 Subjects Initially, 24 healthy young males and 23 healthy young females, who were habitually active in resistance training (at least one session per week), agreed to participate in the study. Inclusion criteria were as follows: (1) aged 20–35 years; (2) proficiency in back squat and bench press exercises from ≥1 year of experience in regular resistance training; and (3) motivated and able to commit to a supervised 8-week VBRT intervention. Exclusion criteria were as follows: (1) injury or illness that might influence intense training of the lower and upper limbs; (2) being a competitive athlete in a specific sport; and (3) use of any medication/substance that might influence neural, musculoskeletal or endocrine system function (with the exception of oestrogen/progesterone-containing oral contraception in females). Before study initiation, subjects undertook an evaluation by a medical physician, including a resting ECG test and medical history, to assess suitability. Once cleared for participation, the subjects were fully informed of all study requirements, methodology, possible harms and discomforts and were given the opportunity to discuss the study with the research team. Thereafter, they signed informed consent. Subsequently, 21 males and 16 females (six using oral contraceptives: three in F20%VL and three in F40%VL) completed all study requirements (for characteristics, see Table 1) and were entered into analyses (Figure 1). The final number of subjects in each group was 11 males training to 20% velocity loss (M20%VL), 10 males training to 40% velocity loss (M40%VL), nine females training to 20% velocity loss (F20%VL) and seven females training to 40% velocity loss (F40%VL). 2.4 Acute loading test protocol Subjects arrived at the laboratory at their allocated time (range 09.00– 20.00 h), which followed 24 h without exercise and 3 h refraining from caffeine. Thereafter, the subjects cycled for 10 min on an ergometer and performed 10 squats without external load as part of their warm-up. To complete the warm-up, subjects performed the Smith-machine (Kraftwerk, Tuusula, Finland) back squat exercise for two sets: one set of six repetitions at 40% of predetermined 1-RM and one set of four repetitions at 50% of 1-RM. Rest times between warmup sets were 2 min, and all concentric actions were performed as fast as possible. Subjects were instructed to perform the eccentric action in a controlled manner (i.e., ∼2 s). A linear velocity transducer (T-Force system; Ergotech, Murcia, Spain) measured the MPV and relayed the data to accompanying software controlled by a laptop, which was monitored in real time by a researcher, who provided velocity feedback to the subject after each repetition and strong verbal encouragement throughout the loadings (Figure 2). The acute loading protocol consisted of five sets at 70% of 1-RM with 3 min recovery between sets, which lasted ∼80 min including all measurements. This loading protocol was designed to match closely the training protocol that the subjects performed in the latter part of the 8-week period and, in particular, the final week (two sessions) of training (Rissanen et al., 2022: their table 2, p. 1271). The sets were terminated once subjects performed a repetition that reached the MPV threshold for their group (VL20% or VL40%), and the number of completed repetitions was recorded. Each concentric action was performed as fast as possible, but the subject was not allowed to jump at full extension. Instead, a slight rise onto the toes was permitted if the subject felt they would otherwise purposefully decelerate the barbell during the lift. The depth of each squat was controlled by an infrared sensor (Faculty of Sport and Health Sciences, University of Jyväskylä, Finland) that emitted a high-pitched sound once the barbell had descended to the preassigned position (Figure 2). The electrical signal generated by the infrared sensor was also synchronized to EMG data to localize the start/end of each concentric action. Foot placement (foot width and heel position) was reproduced for each subject individually by tape markings on the floor. 2.5 Measurements 2.5.1 Countermovement jump height After the completion of the warm-up (PRE and POST24), subjects stood on a custom-built force-plate (Faculty of Sport and Health Sciences, University of Jyväskylä, Finland), with hands on hips. Flight times were determined from ground reaction forces sampled at 1,000 Hz (Signal software v.4.10; Cambridge Electronic Design, Cambridge, UK), filtered by a 10 Hz fourth-order low-pass Butterworth filter, and analysed offline using a customized script. After the command ‘jump’, the subjects descended to a self-selected depth 1050 WALKER ET AL. Laptop monitoring velocity Linear velocity transducer Infra-red sensor unit FIGURE 2 Smith-machine back squat set-up, showing the integration of the linear velocity transducer and infrared sensor in monitoring performance. This experimental set-up allowed real-time monitoring and feedback on concentric lifting performance, in addition to standardization of technique throughout the loading. The images show full extension and the base position of the squat (knee angle of ∼90◦), then extended the legs and trunk as fast as possible. Subjects were instructed to jump as high as possible and to land on the toes with legs fully extended before cushioning the landing. Subjects were given verbal encouragement during each trial. Jump height was calculated from the flight time using the equation: jump height =½g(t/2)2. The trial with the highest jump height (CMJ) was taken forward to further analyses. Three trials were performed before (PRE) and 24 h (POST24) after loading, with 30 s rest between trials, and one trial was performed within 30 s of completing the loading protocol (POST). 2.5.2 Single-pulse twitch and highand low-frequency doublet force Single square-pulse (400 V, 200 μs duration) electrical stimulations were given by a constant-current stimulator (model DS7AH; Digitimer, Welwyn Garden City, UK) to the femoral nerve through 5 cm2selfadhesive square electrodes (V-trode electrodes; Mettler Electronics, Anaheim, CA, USA) placed in the femoral triangle either side of the nerve (identified by palpating and locating the femoral artery). The electrodes were replaced slightly until the greatest unilateral kneeextension twitch force response was achieved with a low stimulation intensity. The intensity was then increased until there were no further increases in force response (typically 400–600 mA). The same stimulus intensity was used at POST that was identified and set at PRE. To ensure maximal activation, an additional 20% current was used to induce two maximum single-pulse twitches in resting conditions, with the best taken into further analyses. Thereafter, six double-pulse stimulations were given in resting conditions, first at an interstimulus interval of 100 ms (i.e., 10 Hz, low frequency) then at 10 ms (i.e., 100 Hz, high frequency). Rest periods of 8–12 s were given between stimulations. At POST, the electrical stimulations began 2 min after completion of the loading protocol. The highest twitch force response to 10 Hz (TF10) and 100 Hz (TF100) were taken for further analysis, in addition to the TF10:TF100 ratio (TF10100). 2.5.3 Voluntary activation level During maximal unilateral (right leg) isometric knee-extension trials (knee angle of 110◦), a 100 Hz doublet was given at the force plateau and 2 s after the cessation of the action (i.e., potentiated doublet). One trial was performed without electrical stimulation, in order to set the target force level for subsequent trials. Two subsequent trials were performed with electrical stimulation procedures at PRE and POST24 (1 min rest between trials), and only one trial at POST, 2 min 30 s after the loading protocol. Voluntary activation level (VA%) was determined by the following equation (Bellemare & Bigland-Ritchie, 1984): VA%= (1−superimposed twitch force −maximum voluntary force resting twitch force )×100. All electrical stimulation trials were recorded by Signal software (v.4.10; Cambridge Electronic Design) after being passed through an analog-to-digital converter (Micro 1401; Cambridge Electronic WALKER ET AL.1051 Design), sampled at 2,000 Hz, and analysed offline by manually positioning cursors identifying electrically induced force increases without filtering. 2.5.4 Bilateral isometric leg press Subjects sat in a custom-built electromechanical isometric leg-press device (Faculty of Sport and Health Sciences, University of Jyväskylä, Finland), with a hip angle of 110◦and knee angle of 107◦. After being instructed to push as fast and as hard as possible, subjects were given the commands, ‘Ready, set, push!’. The subjects inhaled on ‘set’ but remained completely relaxed before the instruction, ‘Push!’. The subjects maintained a forceful isometric leg-extension action for ∼3s while being given strong verbal encouragement. Force was recorded at 2,000 Hz, filtered by a 20 Hz fourth-order low-pass Butterworth filter, and analysed offline using a customized script (Signal v.4.10; Cambridge Electronic Design). Three trials were performed at PRE and POST24, with 30 s rest between trials. The POST measurements were taken 3 min after the completion of the loading protocol, and only one trial was performed. The maximum force (MVC) was obtained from the highest instantaneous force value minus the pre-existing force attributable to the weight of the legs. Cursor positions used to determine average force over 100 ms (F100) were inspected to ensure accurate identification of the beginning of force production. The best trial according to MVC and F100 was taken for further analysis. 2.5.5 Mean propulsive power at 60% 1-RM Subjects completed the battery of tests by performing one set of three squat repetitions at 60% of 1-RM at PRE and POST24. The concentric phase was performed as fast as possible. This test set was repeated 5 min after the completion of the loading (POST). The MPV was measured by a transducer attached to the barbell interfaced to a 14-bit analog-to-digital data-acquisition board and custom software (T-Force System; Ergotech, Murcia, Spain). Velocity was sampled at 1,000 Hz, and a 10 Hz fourth-order low-pass Butterworth filter with no phase shift was used to acquire data in real time. The propulsive phase was defined as the portion of the concentric phase during which barbell acceleration is greater than the acceleration attributable to gravity (Sánchez-Medina et al., 2010). Repeatability of the device and analysis methods have been reported elsewhere (Courel-Ibáñez et al., 2019). The highest MPV from one of the three trials was taken forward to further analyses. Mean propulsive power (MPP) was derived from the product of the external load and MPV. 2.5.6 Muscle activity during countermovement jump, isometric leg press and squat Self-adhesive bipolar Ag/AgCl surface EMG electrodes (5 mm diameter, 20 mm inter-electrode distance; Ambu BlueSensor N, Copenhagen, Denmark) were secured to the skin of the vastus lateralis (VL) and vastus medialis (VM) after skin preparation in accordance with Surface ElectroMyoGraphy for the Non-Invasive Assessment of Muscles (SENIAM) project guidelines. Electrode placement was in line with the orientation of the underlying fascicles and marked by indelible ink tattoos (Häkkinen & Komi, 1983) to ensure accurate replacement after the training period. Raw signals were sent from a hip-mounted pack to a receiving box (Telemyo 2400R; Noraxon, Scottsdale, AZ, USA), then relayed to an analog-to-digital converter (Micro 1401; Cambridge Electronic Design) and recorded at 2,000 Hz by Signal v.4.10 software (Cambridge Electronic Design). The EMG signals were amplified at a gain of 500 (bandwidth 10–500 Hz, common mode rejection ratio >100 dB, input impedance >100 MΩ, baseline noise <1μV root mean square) and sampled. Offline analyses were conducted using customized scripts, in which the signals were filtered using a 20–350 Hz bandpass, and the concentric phase of the countermovement jump (CMJEMG) and back squat (MPPEMG) tests were identified and isolated for concentric root mean square EMG amplitude assessment. For isometric leg-press trials, root mean square EMG amplitude was taken from 0 to 100 ms (F100EMG) and from 500 to 1,500 ms (MVCEMG) after the beginning of force production. The EMG amplitudes of vastus lateralis and medialis were inspected individually, were combined and averaged (VL +VM/2) as a representation of superficial vastii activity. 2.5.7 Serum hormone concentrations Venous blood samples (5 ml blood into Venosafe serum tubes; Terumo Medical, Leuven, Belgium) were collected from the antecubital vein. Samples were collected before EMG preparation and warm-up (PRE) and 10 min after (POST) the loading protocol. Basal samples, after overnight fast, were also collected between 07.00 and 08.00 h on the morning of the acute loading test (PREbasal) and again after fasting between 07.00 and 08.00 h on the morning after the loading (POSTbasal). Samples were centrifuged for 10 min at 4◦C, 2,000×g (Megafuge 1.0R; Heraeus, Germany) to separate the serum and stored at −80◦C until analyses. Immunometric chemiluminescence techniques were used (Immulite 1000; Siemens, IL, USA) with hormone-specific immunoassay kits to determine total testosterone (T), cortisol (COR) and human growth hormone (GH) concentrations. In addition to hormones, the creatine kinase (cK) concentration was obtained from the same serum sample and using the same methods. Data presented are uncorrected for changes in plasma volume. In our laboratory, analytical sensitivity is T =0.5 nmol L−1,GH=0.01 μgL −1, COR =5.5 nmol L−1and cK =3.9 pg mL−1, and the intra-assay coefficient of variation is T =13%, GH =5.8%, COR =7.9% and cK =5.9%. 2.5.8 Blood lactate Fingertip samples were taken before EMG preparation and warm-up (PRE), 1 min 30 s after (POST1) and 10 min after (POST10) the loading protocol. Samples (20 μl) were collected into capillary tubes, which 1052 WALKER ET AL. TABLE 2 Performance (mean ±SD) during acute loading tests 1 (before the training period) and 2 (after the training period) Training Test Load (kg) Average number of repetitions Average concentric velocity (m s−1) Average velocity loss (%) Total mechanical work (J) M20%VL 1 79.5 ±20.5 5.1 ±1.5 0.66 ±0.06 19.5 ±1.0 1,519 ±502 2 84.5 ±23.7*4.4 ±0.8 0.72 ±0.07 21.7 ±1.1*1,220 ±164 M40%VL 178.9 ±9.6 7.1 ±1.3 0.56 ±0.03 42.1 ±3.3 2,108 ±457 285.6 ±11.7*6.0 ±1.9 0.60 ±0.04*40.5 ±1.1 1,826 ±642 F20%VL 1 45.9 ±9.1†4.6 ±1.4 0.60 ±0.08 20.5 ±1.3 760 ±279† 2 50.4 ±10.0*†4.4 ±1.0 0.67 ±0.08*20.1 ±1.8 735 ±223 F40%VL 144.3 ±9.7†7.9 ±2.6 0.53 ±0.07 41.3 ±4.2 1,323 ±512† 250.4 ±10.2*†6.3 ±2.3 0.56 ±0.09 41.3 ±2.1 1,072 ±446† Abbreviations: M20%VL, males training to 20% velocity loss per set; M40%VL, males training to 40% velocity loss per set; F20%VL, females training to 20% velocity loss per set; F40%VL, females training to 40% velocity loss per set. *P<0.05 compared with acute loading test 1. †P<0.05 compared with the male group with the same assigned velocity loss (i.e., M20%VL vs. F20%VL and M40%VL vs. F40%VL). were placed into a 1 ml haemolysing solution and analysed according to the manufacturer’s instructions (EKF diagnostic, C-line system, Biosen, Germany) on the day of sample collection. 2.6 Statistical analyses All statistical procedures were performed using SPSS v.26 software (IBM statistics, IBM, Armonk, NY, USA). Standard procedures were used to determine descriptive statistics, and all data are reported as the mean ±SD, unless otherwise stated. Before analyses, tests of normality (Shapiro–Wilk) were run to ensure that the assumptions for parametric statistics were upheld. Hormone and EMG amplitude data were not normally distributed and were log10-transformed before performing statistical analyses (data are presented in their original form). Repeated-measures ANOVA (three times ×four groups ×two loadings) was used to evaluate the effects of the loading between sexes and velocity-loss protocols for all except serum hormone variables. In this case, comparisons were made for two time points, either PRE versus POST or PREbasal versus POSTbasal (repeated-measures ANOVA: two times ×four groups ×two loadings). In the majority of analyses, sphericity was not observed, hence Greenhouse–Geisser adjusted degrees of freedom for within-group comparisons were applied when calculating main effects for time, time ×group, time × loading and time ×group ×loading. When a significant F-value was observed, post hoc tests were performed with Bonferroni adjustments to locate the source of the difference. The value of αwas set at 0.05. 3RESULTS 3.1 Performance during acute loading test 1 and 2 Tabl e 2shows the performance during each loading test for the four groups. Significant main effects for loading and group were observed in load (F1=70.4, P<0.001 and F3=16.5, P<0.001, respectively), average number of repetitions per set (F1=10.2, P=0.003 and F3=7.7, P<0.001, respectively), average concentric velocity of all repetitions (F1=22.7, P<0.001 and F3=10.3, P<0.001, respectively) and total mechanical work (F1=8.4, P=0.007 and F3=17.8, P<0.001, respectively). Average velocity loss per set showed a main effect for loading ×group (F3=3.7, P=0.022). Post hoc tests revealed that load and, in turn, mechanical work, was greater for males than for females (Table 2). Furthermore, there were significant differences in total mechanical work between M20VL and M40VL during acute loading test 1 (P=0.03) and 2 (P=0.011), but there were no differences in total mechanical work between F20%VL and F40%VL. 3.2 Maximal voluntary dynamic and isometric performance The MPP showed significant main effects for time (F2,1.89 =13.6, P<0.001), time ×group (F6,5.46 =2.7, P=0.021), group (F3=28.2, P<0.001) and loading (F1=8.1, P=0.006). Post hoc tests revealed that M40%VL decreased MPP at POST compared with PRE (P=0.037) during acute loading test 1. This reduced MPP was recovered at POST24 (Figure 3a). Conversely, MPP decreased in M20%VL at POST compared with PRE (P=0.009) during acute loading test 2. No changes in MPP were observed in females. The CMJ showed significant main effects for time (F2,1.95 =207.5, P<0.001), time ×group (F6,5.84 =4.0, P=0.001), group (F3=35.1, P<0.001) and loading (F1=4.6, P=0.036). Post hoc tests revealed that all groups decreased CMJ at POST compared with PRE (P<0.05; Figure 3b) during both acute loading test 1 and test 2. The CMJ had recovered at POST24 in all groups after both loading tests. The MVC showed significant main effects for time (F2,1.92 =205.9, P<0.001), group (F3=18.1, P<0.001) and time ×group (F6,5.76 =7.4, P<0.001). Post hoc tests revealed that all groups decreased MVC at POST compared with PRE (P<0.05; Figure 3c) during both acute WALKER ET AL.1053 (a) M20% 120 110 100 90 80 80 60 40 50 70 60 0 0 0 M40% Acute loading test 1 MPP during 60% 1-RM squat Maximum isometric leg press force Isometric leg press force 0-100 ms Countermovement jump height MPP (% of pre-loading) (b) (d) 160 140 120 100 100 200 250 150 CMJ (% of pre-loading) F100 (% of pre-loading) (c) 120 110 100 90 80 70 60 0 MVC (% of pre-loading) F20% F40% M20% M40% Acute loading test 2 F20% F40% M20% M40% Acute loading test 1 F20% F40% M20% M40% Acute loading test 2 F20% F40% M20% PRE POST POST24 PRE POST POST24 PRE POST POST24 PRE POST POST24 M40% Acute loading test 1 F20% F40% M20% M40% Acute loading test 2 F20% F40% M20% M40% Acute loading test 1 F20% F40% M20% M40% Acute loading test 2 F20% F40% FIGURE 3 Mean (white bars) and individual data for voluntary neuromuscular performance, relative to pre-loading levels, during acute loading tests 1 (before the training period) and 2 (after the training period) in mean propulsive power (MPP) in back squat (a), countermovement jump height (CMJ; b), maximum bilateral isometric force (MVC; c) and isometric force over the initial 100 ms (F100; d) in the leg press. *P<0.05 compared with pre-loading. Abbreviations: 1-RM, one-repetition maximum; POST24, 24 h after loading loading test 1 and test 2. However, M40%VL had not recovered MVC at POST24 after acute loading test 1 (P=0.022) or test 2 (P=0.009). A similar trend was also observed for F40%VL at POST24 after acute loading test 1 (P=0.073). The F100 showed significant main effects for time (F2,1.85 =27.1, P<0.001), group (F3=5.3, P=0.003) and time ×group × loading (F6,5.56 =2.2, P=0.05). Post hoc tests revealed that only M40%VL reduced F100 at POST compared with PRE (P=0.001) during acute loading test 1, which remained decreased at POST24 (P=0.001; Figure 3d). After acute loading test 2, both M20%VL and M40%VL decreased F100 at Post compared with PRE (P<0.05), and also F20%VL showed decreased F100 at POST compared with PRE (P=0.048), with F40%VL trending to decrease (P=0.066). All had recovered at POST24. 3.3 Voluntary muscle activity The MPPEMG showed significant main effects for time ×loading (F2,1.85 =27.1, P<0.001) and time ×group ×loading (F6,5.56 =2.2, P=0.05). Post hoc tests did not reveal significant within-group changes in MPPEMG at any time point during acute loading tests (Table 3). Also, there were no significant main effects observed for CMJEMG. The MVCEMG showed significant main effects for time (F2,1.34 =27.1, P<0.001) and group (F3=7.7, P<0.001). Post hoc tests revealed that only M20%VL decreased MVCEMG at POST compared with PRE (P=0.002) during acute loading test 1. However, all groups demonstrated decreased MVCEMG at POST compared with PRE during acute loading test 2 (P<0.01; Table 3). The F100EMG showed significant main effects for time (F2,1.97 =5.8, P=0.004) and time ×group (F6,5.92 =3.6, P=0.003). Post hoc tests did not reveal significant within-group changes in F100EMG at any time point during acute loading tests (Table 3). 3.4 Twitch responses and voluntary activation level The TF10 showed significant main effects for time (F2,1.66 =216.8, P<0.001), group (F3=6.7, P=0.001) and time ×group (F6,4.98 =6.9, P<0.001). Post hoc tests revealed that all groups decreased TF10 at POST compared with PRE (P<0.05; Figure 4a), but only F40%VL showed reduced TF10 at POST24 (P=0.01) after acute loading test 1. After acute loading test 2, all groups decreased TF10 at POST compared with PRE (P<0.01), but both male groups showed reduced TF10 at POST24 (P<0.01). The TF100 showed significant main effects for time (F2,1.62 =66.7, P<0.001), group (F3=15.0, P<0.001) and time ×group (F6,4.86 =3.3, P=0.009). Post hoc tests revealed that both male groups decreased TF100 at POST compared with PRE (P<0.01; Figure 4b) after acute loading test 1. 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SUPPORTING INFORMATION Additional supporting information can be found online in the Supporting Information section at the end of this article. How to cite this article: Walker, S., Häkkinen, K., Virtanen, R., Mane, S., Bachero-Mena, B., & Pareja-Blanco, F. (2022). Acute neuromuscular and hormonal responses to 20 versus 40% velocity loss in males and females before and after 8 weeks of velocity-loss resistance training. Experimental Physiology,107, 1046–1060. https://doi.org/10.1113/EP090371