Resistance training is widely recognized as an effective method for improving athletic performance due to documented adaptations in muscular hypertrophy, maximal strength, rate of force development, and power output (28). The specific adaptive response to resistance training has been shown to be directly influenced by the configuration of a number of acute training variables, including loading magnitude, number of sets and repetitions, rest duration, and exercise type (23). Although the optimal combination of these training variables remains an area of interest, it seems that relative load and training volume (sets × repetitions) are the 2 most critical factors in determining the type and extent of resulting neurophysiological adaptations (14,29).
Although differing methods for determining training load exist, the most common method, traditionally known as percentage-based training (PBT), prescribes relative submaximal loads from a previously established 1 repetition maximum (1RM). This method is prevalent within the literature and has been shown to be valid and reliable across a range of populations (24). However, as maximal strength has been shown to fluctuate daily due to fatigue, and significantly increase due to continuous training, the method of prescribing relative load on potentially obsolete 1RMs has been questioned (11,15). Other methods, collectively referred to as autoregulatory, rely on an athlete's understanding of their rating of perceived exertion or “repetitions in reserve” (16). These methods offer real-time load adjustment, based on an athlete's perceived readiness to train. Although considered valid and reliable with trained populations, autoregulatory methods adjust load based on subjective input from the athlete, creating potential inconsistencies between athletes and sessions based on understanding. Furthermore, although these methods facilitate load adaptation within training, they require a minimum number of repetitions to be completed before interpretation, potentially fatiguing participants before load modification (16). Therefore, an alternative method able to provide instantaneous repetition feedback, enabling objective load modification, could augment adaptations while concurrently limiting training-induced fatigue.
A potential alternative, made more accessible with recent advancements in commercially available kinematic measuring devices, exploits the relationship documented between relative load and mean concentric velocity (MCV) (15,18). Research has demonstrated that movement velocity, which is dependent on both the magnitude of the load, and the voluntary intent to move it (7) influence neuromuscular stimuli and, thus, the adaptations consequent to resistance training. This load-velocity relationship, commonly termed the load-velocity profile (LVP), has been explored across a range of compound movements including bench press, back squat, and prone bench pull (9,15,26). Providing maximal concentric effort is applied during movement, an inverse linear relationship is present between load and MCV. Furthermore, as repetitions continue during a consistent range of motion, MCV will decrease as muscular fatigue develops. This understanding has made it possible to determine the relative load during a given movement in relation to an athlete's current daily maximum and their MCV, providing an LVP has been established (15). Such findings have opened up the possibility of real-time monitoring of relative load, enabling specific adaptations to be targeted, factoring in training fatigue and strength fluctuations, as repetitions, sets, and periodization progresses.
Importantly, although LVPs have been shown to be reliable across repeat visits with trained athletes (5), limited research has explored the use of integrating LVPs into periodized resistance training as a method of adjusting training load. Previous literature exploring velocity-based training (VBT) has used the LVP as a means to prescribe load at a given concentric velocity, with participants instructed to complete all repetitions maximally. This maximal concentric method has been compared with various training modalities, with results generally supporting its use as a means to elicit adaptations in strength and power performance (12,13,20,22). Despite these prospective improvements, methodological discrepancies between the research designs limit the confidence surrounding the proposed conclusions. Issues such as lack of training variable control, participants training experience, use of a Smith machine as opposed to free-weight movements, undisclosed maturation status of youth participants, or unreliable velocity collection methods are present throughout. Furthermore, to date, no research has explored the effect of VBT when compared with traditional PBT methods.
Despite the perceived and demonstrated importance of lifting velocity and its relationship with optimal load prescription, no research currently exists comparing the effects of manipulating load based on a pre-established LVP. Therefore, the aim of the present research was to investigate the effects VBT have on the strength and power adaptations within resistance-trained men when compared with a traditional PBT approach. This aim was achieved through the implementation of MCV monitoring into a periodized resistance training program over a 6-week mesocycle. Addressing this will provide further insight into researchers and practitioners in making informed decisions about the use of velocity as a performance variable within athletic program design and monitoring.
Experimental Approach to the Problem
A randomized controlled research design was used to explore the effects of manipulating load, based on MCV, within a resistance training program. After familiarization and pretesting, participants were randomly assigned to either a VBT or PBT training intervention. All participants completed 2 training sessions each week, over a 6-week mesocycle, before repeating the testing battery after intervention. Testing consisted of a series of free-weight, 1RM strength tests, including back squat, bench press, overhead press, and conventional deadlift, and a countermovement jump (CMJ) protocol. All tests were performed at least 96 hours before/after the most recent training session. All testing and training took place at the same venue, under the direct supervision of the lead investigator, at the same time of the day (±1 hour) for each subject, and under constant environmental conditions (∼20° C).
Thirty men originally volunteered to take part in the research study; however, due to injury (n = 3) and failure to meet the inclusion criteria (n = 11), 16 resistance-trained men were recruited and completed the training intervention (mean ± SD, age: 22.8 ± 4.5 years [age range: 18-30 years old], stature: 180.2 ± 6.4 cm, and body mass: 89.3 ± 13.3 kg). Participants' 1RM for the back squat, bench press, strict overhead press, and deadlift was 140.2 ± 26.0 kg, 107.7 ± 18.2 kg, 61.3 ± 8.7 kg, and 176.6 ± 27.2 kg, respectively (i.e., 1.54 ± 0.29, 1.13 ± 0.20, 0.68 ± 0.10, and 1.95 ± 0.30, respectively, when normalized to body mass). It was required that all subjects had at least 2 years of resistance training experience and had been engaged in continuous resistance training for at least 6 months before the program start date. After medical screening and experimental outline, written informed consent was obtained from each participant, with previous approval from the University of Lincoln ethics committee, in line with the Helsinki Declaration for research with human volunteers.
Before all testing and training sessions, participants were supervised during a standardized warm-up, consisting of 5 minutes of stationary cycling (Wattbike, West Bridgford, United Kingdom; 60 rpm, 60 W), followed by an additional 5 minutes of self-prescribed dynamic stretching and barbell mobility work.
Jumps were calculated at the nearest 0.1 cm, using a Just Jump mat (Probiotics, Huntsville, AL), with the subject holding a 0.4-kg dowel behind their head (back squat position (10)). The dowel was required to remain in contact with the participant's trapezius throughout the full trial. During each attempt, at a self-selected pace, participants would squat to their perceived optimum depth before immediately driving upward, with the aim of attaining maximum vertical height. Participants were instructed to keep legs straight throughout the airborne phase, with any deviation from this resulting in a void trial. A total of 3 trials were completed, interspaced with 3-minute rest.
One Repetition Maximum
For both the back squat and bench press, 1RM was established following the same procedures. Participants completed an initial set of 8–10 repetitions with the empty bar, followed by 5–6 repetitions at ∼50% estimated 1RM. This was increased to ∼70% estimated 1RM for 3–5 repetitions, and finally ∼90% estimated 1RM for a single repetition. At this stage, the researcher dictated incremental load increases, until 1RM was achieved using correct technique, through a full range of motion. For all repetitions, subjects were instructed to maintained eccentric control, before generating maximal force during the concentric phase. Achievable load increases were selected, with the aim of attaining a true RM within 3 to 5 attempts. If an attempt was failed, the load was decreased until a single repetition was completed. Each series of repetitions throughout the full protocol was interspaced with 3–5 minutes of rest. During each incremental load, a linear positional transducer (GymAware PowerTool; Kinetic Performance Technology, Canberra, Australia) was attached to the barbell, allowing for the calculation of MCV. Furthermore, the GymAware PowerTool was used to monitor depth during the back squat, ensuring participants maintained a consistent depth during all repetitions during the protocol.
For both the strict overhead press and deadlift, 1RM and velocity profiling were established following procedures similar to those described by Sánchez-Medina et al. (26). For both exercises, initial load was set at ∼30% estimated 1RM, or 20 kg (empty bar), with incremental increases of ∼5% estimated 1RM after completion of successful repetitions. For light loads (≤50% estimated 1RM), participants completed 3 repetitions, decreasing to 2 repetitions for medium loads (55–75% estimated 1RM), and a single repetition for high loads (≥80% estimated 1RM). For all repetitions, subjects were instructed to maintain eccentric control, before generating maximal force during the concentric phase. Strong verbal encouragement and velocity feedback were provided to motivate subjects to give maximal effort throughout. If participants continued to successfully complete repetitions after achieving their estimated 1RM, incremental load increases were applied until a true 1RM was achieved. For all repetitions, MCV was calculated and recorded through the use of the GymAware PowerTool.
Resistance Training Program
All participants completed 2 resistance training sessions per week, for 6 continuous weeks. For both training groups, the base program (Table 1) was devised based on methods previously described by Baker (2–4), following a wave-like periodization structure. Relative training loads (% 1RM), number of sets, and interset rest time were equal between groups throughout the 6-week intervention. In addition to the assessed compound movements (back squat, bench press, strict overhead press, and deadlift), supplementary exercises were included within the training intervention. To ensure consistency between groups, sets and repetitions were equated, with load dictated using specific equations, using body mass, or through use of a repetitions in reserve approach (Table 1; (16)). All participants were given strong verbal encouragement throughout repetitions to motivate them to give maximal effort throughout.
To successfully integrate velocity monitoring into the base resistance training program for the VBT group, a combination of velocity zones and velocity stops was used (19,23). For the key movements (back squat, bench press, strict overhead press, and deadlift), MCV monitoring was used to dictate changes in load lifted, and number of repetitions completed, on a real-time, set-by-set basis. Group zones for each movement were created using a combination of previously published data (15,21,26,27) and data collected within the pretesting 1RM assessments. From this consolidation of data, specific group velocity zones were calculated for each movement, for each relative load (i.e., 70% 1RM, back squat: 0.74–0.88 m·s−1; bench press: 0.58–0.69 m·s−1; strict overhead press: 0.77–0.91 m·s−1; deadlift: 0.51–0.65 m·s−1). Velocity stops were integrated into each set at 20% below the target velocity of each specific zone (23).
During each repetition, VBT participants were provided with real-time auditory feedback based on the MCV of each repetition in relation to the predetermined zone. The MCV of the completed repetitions (relative load <80% 1RM: 2 repetitions; relative load >80% 1RM) was then reviewed in comparison with the relative velocity zone data. If the velocity was within the zone, the sets continued as programmed, and if the velocity was above or below the zone, the subsequent load was adjusted based on the load-velocity relationship profiles. This meant that load increments/decrements were not standardized and instead specific to the athlete's current performance in comparison with the group LVP.
For all variables, values are presented as mean ± SD. Data analysis was completed using SPSS 22.0 (Chicago, IL, USA), with the alpha level for significance set at α = 0.05. Independent-samples t-tests were completed to examine the pre-training intergroup differences and post-training total volume relationship. Paired-samples t-tests were completed to examine the intragroup percentage difference pre-training to post-training. Two-way mixed (between-within) analysis of variance, with Bonferroni post hoc comparisons, using 1 interfactor (VBT vs. PBT) and 1 intrafactor (pre-training vs. post-training), was conducted to examine the differences across all compound movements and jump protocols between groups. In addition, effect sizes (ESs) were calculated according to the Cohen scale (8). Calculating ES allows the intergroup differences to be quantified irrespective of sample size. According to Cohen (8), ES can be classified as small (d = 0.2), medium (d = 0.5), and large (d = 0.8), thus inferring that when group mean values do not differ by greater than 0.2 SDs, the difference is trivial.
No significant differences between the VBT and PBT groups were reported before training for any variables analyzed, including body mass, 1RM strength, and CMJ height.
For both training groups, compliance within the program was 100% of all scheduled sessions. Descriptive characteristics and ES are presented within Table 2. Training resulted in significant increases in maximal strength for back squat (VBT 9%, PBT 8%), bench press (VBT 8%, PBT 4%), strict overhead press (VBT 6%, PBT 6%), and deadlift (VBT 6%; Figure 1). No significant group by time interaction effects were witnessed between training groups for the back squat, strict overhead press, or deadlift. A significant group by time effect (F (1,14) = 11.50, p = 0.004) was recorded between groups for the bench press, indicating a significantly greater increase in maximal strength after the VBT intervention when compared with the PBT intervention.
Vertical Jump Assessment
A significant group by time effect (F (1,14) = 7.14, p = 0.018) was present between training groups for CMJ (Figure 1). Training resulted in a significant increase in CMJ performance for the VBT group (5%) but not the PBT group (1%).
Intended vs. Actual Total Volume
The VBT group completed significantly less volume for the back squat (9%), bench press (6%), and strict overhead press (6%) when compared with the PBT group (Table 3).
The aim of the present research was to investigate the impact of 2 different load prescription methods over a 6-week resistance training intervention on strength and power in trained men. The data presented provide sufficient evidence to support the use of velocity-based loading methods within a resistance-trained population for eliciting favorable adaptations in maximal strength and vertical jump height when compared with traditional percentage-based loading methods. This finding is furthered when considering the significant reduction in volume completed by the VBT group over the intervention compared with the PBT group, specifically across the back squat, bench press, and strict overhead press exercises.
Findings from this research revealed training-induced adaptations in maximal strength and jump height after 6 weeks of VBT. Although no direct comparative research is currently available, the results of this study are in agreement with previous investigations that reported increases in strength or vertical jump performance after similar VBT interventions. Pareja-Blanco et al. (22) demonstrated the importance of velocity within resistance training, comparing maximal velocity to deliberate “half-velocity” training. After a 6-week intervention, back squat 1RM significantly improved in both groups (maximal velocity: 18.0%; half-velocity: 9.7%), with a group by time trend approaching significance. Furthermore, significant adaptations were recorded for CMJ in the maximal velocity group only (+8.9%), producing a significant group by time interaction. In a similar context, González-Badillo et al. (13) reported significant increases in bench press 1RM after 6 weeks of maximal velocity resistance training when compared with “half-velocity” training. Both groups (recreationally trained males; n = 20) saw significant improvements (maximal velocity: 18.2%; half-velocity: 9.7%) pre-training to post-training, with the maximal velocity group producing significantly greater adaptations. Further research (23) explored the outcome of 8 weeks of VBT, comparing the effects of velocity loss on 1RM back squat and CMJ performance. Participants (healthy men; n = 22) completed identical training programs, only differing in velocity stop cutoff for each exercise (20% vs. 40%), and thus potential total repetitions. Significant maximal strength adaptations were recorded in both the 20%, and 40% group (18.0% vs. 13.4%, respectively), with no group by time effect recorded. Further significant adaptations were witnessed in the 20% group for CMJ (9.5%), with negligible improvement witnessed in the 40% group (3.5%), resulting in a significant group by time effect.
Although the training-induced effects and levels of percentage change reported in the aforementioned research are greater than those witnessed in the current investigation, this can be attributed to a number of methodological disparities. First, all the investigations discussed used recreationally trained men (back squat 1RM: 92.1 ± 10.4 kg (22); 106.2 ± 13.0 kg (23); bench press 1RM: 74.9 ± 13.8 kg (13)) as opposed to the current study, where resistance-trained men were used (back squat 1RM: 140.2 ± 26.0 kg; bench press 1RM: 107.7 ± 18.2 kg). The training status of individuals is known to have a significant effect on the resultant adaptations witnessed after a training intervention (1,25,28). Lesser trained participants have been shown to generate significantly greater adaptations when compared with trained individuals, directly impacting on this comparison of data. This has been linked to increased neural alterations occurring at an accelerated rate in lesser trained participants, such as greater synchronization and recruitment of motor units, improved rate coding, and greater reflex potentiation (6). As participants in the current study were already resistance-trained, these neural mechanistic changes are not witnessed to the same extent, impacting on the overall post-training adaptations. Furthermore, in two of the comparative investigations (13,22), control participants were instructed to deliberately slow their repetitions to that of ∼50% maximal MCV, which has been shown to have a significant effect on the adaptations witnessed (23). In the current study, both groups were instructed to maintain eccentric control before immediately lifting the load, using a 3-second eccentric phase, minimal pause, followed by an immediate concentric phase. The only differing factor was the use of MCV to dictate load and repetitions within the VBT group.
The data presented further suggest that using MCV as a means to determine load and repetitions results in a significant reduction in required training volume to produce favorable adaptations in maximal strength and jump performance. Recent literature (23) established how continued repetitions, and thus a decrease in lifting velocity, can alter the adaptations witnessed when compared with a higher velocity program, with lower total volume. After completion of a VBT program, with either low (20%; V20) or high (40%; V40) velocity stop cutoff, participants completed a 1RM squat protocol. Although within-subject pre-training to post-training statistical differences were present (V20: 18.0% vs. V40: 13.4%), no group by time interaction was recorded. However, a significant difference was present between the total repetitions completed by each group (V20: 185.9 ± 22.2 vs. V40: 310.5 ± 42.0) and the total work completed (V20: 127.5 ± 15.2 kJ vs. V40: 200.6 ± 47.1 kJ), highlighting the importance of concentric mean velocity monitoring within resistance training. Although the V20 group did not significantly improve over the V40 group, the lower volume, higher velocity training, elicited favorable adaptations while reducing the likeliness of training-induced fatigue (17). Within the present data collection, the VBT group lifted significantly less volume than the PBT group, for back squat (9%), bench press (6%), strict overhead press (6%), and consequently, overall (6%), however produced similar (back squat, strict overhead press), or statistically greater (bench press) adaptations. It is worth noting that training programs were initially designed with equated total volume (sets × repetitions × relative load); however, as the VBT groups load and repetitions were dictated through real-time MCV monitoring, deviations from this equated volume occurred. This variance of total lifting volume was allowed to occur, as it was deemed a true representation of VBT and how MCV impacts other training variables.
In summary, the data presented within this investigation suggest that using velocity as a performance variable and means of dictating load may provide greater maximal strength adaptations than traditional percentage-based loading methods. The combination of velocity zones and stops used provided a favorable environment for strength and power adaptations within a resistance-trained population. Furthermore, the results suggest that providing a movement is completed with an optimal load (dictated through MCV), fewer repetitions, and thus a lower total training volume is necessary to significantly improve maximal strength, and more pertinent to sporting performance, allow a positive transfer effect to movements including vertical jump.
The results of this study contribute to the awareness surrounding VBT interventions within a resistance-trained population and, specifically, the use of MCV as a means to alter training load. The data presented increase confidence surrounding the practical use of velocity zones and stops within a periodized resistance training program and how these can be used to improve muscular strength and power. Furthermore, prescribing and monitoring training intensity through MCV provides greater control over the prescribed training load and the participants' current state of fatigue, without the need to perform multiple RM protocols.
The authors thank the subjects for their participation within the study. The data presented do not constitute to the endorsement of the methods discussed by the authors or the National Strength and Conditioning Association.
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