The effect of real-time visual feedback and verbal encouragement on repetition velocity of squat,bench press and deadlift exercises in competitive powerlifters

Introduction

Athletes and coaches often use resistance training to increase muscle mass and improve strength and power. These adaptations can lead to better performance in sports that require actions such as sprints, jumps, and changes of direction. ¹ On the other hand, in some sports, such as powerlifting, results are primarily dependent on the athlete's maximal strength. ² Thus, resistance training must be individually customized to achieve specific adaptations based on individual needs.

Resistance training can be tailored to prioritize specific adaptations by adjusting variables such as volume, load, pause, rest, and repetition velocity. ³ Increasing training volume with wide range of loads can produce better results for muscle growth, ⁴ while moderate loads and high concentric velocities are recommended for power, ⁵ and training closer to one's maximal strength (1RM) is preferable to increase maximal strength. ⁶

Although counterintuitive, powerlifters do not often use high-load, but train with moderate loads throughout the year. ⁷ Nevertheless, there is a suggestion that increasing movement velocity during training may provide optimal stimuli to improve maximal strength, ⁸ even when using moderate loads. ⁹ Thus, strategies to increase repetition velocity are perceived as beneficial to powerlifters to improve their maximal strength.

Verbal encouragement, which was shown to enhance repetition velocity, ¹⁰ has been used by coaches to encourage athletes to lift at their maximum concentric velocity. However, many powerlifters train without the supervision of their coaches, which prevents coaches to verbally encourage them. Another strategy to help athletes increase velocity is to allow them to visualize the velocity of each repetition. In such cases, portable and user-friendly linear encoders can be used to display repetition velocity in real-time on a screen, providing visual feedback of the repetition velocity to the athlete. This feedback has been shown to increase movement velocity in comparison to a control condition (i.e., without feedback).^10,11

Although these results provide important information, they are still limited to the performance of only one set in one exercise, and little is known about the effects of real-time feedback during an ordinary training session, consisting of multiple sets and exercises. Also, it has been suggested that athletes have less room for improvements in performance and motivation compared to non-athletes, and thus strategies to increase performance and/or motivation may not be noticeable during a training session.

Thus, the purpose of the current study was to compare repetition velocity in a training session with squat, bench press and deadlift when athletes receive real-time visual feedback of repetition velocity or verbal encouragement with a no-feedback control condition. Our hypothesis was that when athletes train with real-time visual feedback and with verbal encouragement repetition velocity would be higher compared to when they train without any feedback.

Methods

Results

Figure 1 displays results of repetition velocity for each set in each condition. There was no set effect for mean velocity in the squat (p = 0.985), bench press (p = 0.116) and deadlift exercise (p = 0.336). However, condition effect was observed. In the squat exercise, repetition velocity was higher in VE compared to Control (VE = 0.63 ± 0.05 m.s⁻¹, Control = 0.61 ± 0.07 m.s⁻¹, p = 0.0036; ES = 0.35, CI = 0.12–0.59) and in VF compared to Control (VF = 0.64 ± 0.05 m.s⁻¹, p < 0.0002; ES = 0.45, CI = 0.22–0.69). Repetition velocity in the bench press was higher in VE vs Control (VE = 0.43 ± 0.07 m.s⁻¹, Control = 0.40 ± 0.07 m.s⁻¹, p < 0.04; ES = 0.30, CI = 0.07–0.53) and in VF vs Control (VF = 0.43 ± 0.07 m.s⁻¹, p < 0.02; ES = 0.33, CI = 0.10–0.56). Regarding the deadlift exercise, only VF presented higher velocity than Control (p < 0.005; ES = 0.38, CI = 0.15–0.61; VF = 0.49 ± 0.08 m.s⁻¹, VE = 0.48 ± 0.08 m.s⁻¹, Control = 0.46 ± 0.07 m.s⁻¹). There were no differences between VF and VE in any exercise.

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Figure 1.

Repetition velocity (m.s⁻¹) in the bench-press (A), squat (B) and deadlift (C). * – p < 0.05.

Discussion

The aim of the study was to investigate the effects of visual real-time velocity feedback and verbal encouragement with a no-feedback control condition on repetition velocity during strength training sessions for three multi-joint exercises: squat, bench press, and deadlift in highly-trained powerlifters. The results showed that both visual and verbal feedback conditions led to higher repetition velocity compared to the control condition for the squat and bench press exercises. However, only the visual feedback condition showed higher repetition velocity for the deadlift exercise compared to control. While there has been considerable research conducted on the effects of verbal encouragement in the context of strength training, the investigation of visual feedback in this population has received comparatively less attention.^10,14–16

Our findings revealed notable improvements in mean velocity across different exercises with visual feedback. Specifically, we noted an approximate enhancement of 4% in squat, 8% in bench press, and 7% in deadlift repetition velocity. These results align closely with a study by Weakley et al. ¹⁰ that demonstrated a ∼6% enhancement in mean concentric velocity during back squat repetitions with various forms of feedback provided to semi-professional rugby union players, including verbal encouragement, verbal feedback on repetition velocity, and visual feedback. The study indicated that all three types of feedback contributed to improved barbell velocity.

It is important to consider the training level of participants when examining the effectiveness of feedback on performance during strength training. Trained individuals, such as the powerlifters in our study and the rugby players in Weakley's study, can recruit a higher relative percentage of muscle fibers compared to untrained individuals.^14,17 Additionally, feedback (both visual and verbal) can help trained individuals maximize their potential by reducing velocity loss throughout a set ¹⁰ or maintaining average repetition velocity during a session comprising multiple sets and exercises performed at a moderate intensity, as demonstrated in our study. Inexperienced individuals, on the other hand, might find a high frequency of feedback overwhelming and potentially detrimental to the learning process. ¹⁸ However, since our study focused on trained individuals with powerlifting experience, it likely explains the positive results observed with both types of feedback.

In a study by Jiménes-Alonso et al., ¹⁹ two different protocols with real-time velocity feedback were compared, one emphasizing strength gains (squat and bench press at 75% of 1RM) and the other targeting power gains (countermovement jump and bench press throw at 30% of 1RM). Moderately strength-trained participants underwent two sessions per condition, each lasting a week. The study demonstrated that verbal real-time feedback had a positive impact on velocity output (∼7% in squat and ∼6% in bench press repetition velocity) compared to the control (no-feedback condition). These findings are comparable to ours for squat and bench press under the verbal encouragement condition (approximately 4% and 7%, respectively). However, deadlift performance did not show significant improvements with verbal encouragement. Interestingly, visual feedback, but not verbal encouragement, had a positive effect on deadlift velocity performance compared to the control condition. Displaying each repetition's velocity performance could have increased athletes’ competitiveness and serve as a driving force to push themselves to the limit of each repetition, yielding better results than solely providing verbal encouragement for the deadlift exercise. One potential explanation for the lack of significant effects associated with verbal encouragement during the deadlift exercise is that the movement starts with the ascending phase (i.e., concentric contraction) and does not utilize the stretch-shortening cycle. While verbal encouragement has been shown to enhance performance, particularly in the squat and bench press exercises, its effects may be more noticeable in movements that incorporate a transition from eccentric to concentric contractions, (i.e., stretch-shortening cycle). This, however, needs to be tested.

Visual feedback can be particularly beneficial for athletes who train without the presence of a training partner or a coach. It provides real-time information on the velocity of each repetition, enabling athletes to monitor and adjust their performance for optimal training “quality”. Increasing velocity while using the same weight has been shown to be an effective strategy for improving maximal strength and power, even with submaximal loads. ⁹ Portable devices that display velocity data for each set can serve as valuable tools for enhancing training “quality” and optimizing performance during strength training sessions.

Two hypothesized mechanisms may explain the higher velocities observed when feedback is provided. Firstly, athletes may experience improved motivation towards the task. Secondly, they may focus more on external rather than internal information. ²⁰ Heightened motivation due to instantaneous feedback can optimize neural stimuli and increase motor unit recruitment and/or firing rate, resulting in improved movement velocity. ²¹ It is worth noting that maximal strength performance is influenced not only by physiological adaptations but also by psychological factors. Previous research has shown that psychological strategies can effectively reduce strength inhibitions, resulting in approximately 50% improvement in strength performance. ²² Thus, real-time velocity feedback may have some potential in reducing psychological inhibitions.

It is conceivable that athletes focus on technical/proprioceptive aspects of the lift and when informed that their goal is to perform at the highest possible velocity, focus shift from internal (proprioceptive/technical) to external (velocity). Wilkes and Summers ¹⁶ examined the effects of different strategies for psychological preparation, or “psyching up”, before a performance task, such as strength training. They found that an arousal-focused strategy led to a performance increase of approximately 20%. The specific phrase used in the arousal group encouraged athletes to solely concentrate on the forceful and rapid movement of their leg, while the imagery group was instructed to focus on the technical aspects of extending their leg. The latter group did not show any performance improvement. These findings suggest that directing attention towards the task, such as a repetition velocity, rather than solely focusing on technique or intrinsic factors, may be more advantageous for strength performance. Therefore, our results align with previous studies that have highlighted the importance of psychological factors in strength performance.^16,22

Finally, it has been shown that training with higher velocities at the same relative intensity leads to greater long-term performance enhancements. ²⁰ Nagata et al. ²⁰ showed that collegiate male rugby players who received feedback after each repetition during a 4-week training period trained a higher velocities throughout the study and showed larger strength gains compared to those who received no feedback. Thus, it seems reasonable to assume that when receiving either verbal encouragement or visual feedback performance improvements is superior compared to a no feedback condition.

This study is not without limitations. Firstly, we did not directly measure the participants’ one-repetition maximum (1RM), which introduces uncertainty regarding whether the weight used corresponded exactly to 70% of their 1RM. Instead, we relied on their best performance within the past three months and utilized the weight prescribed by the coach for their actual percentage-based intensity, which provides a reasonable estimate of their actual 1RM. Additionally, the same weight was used in all experimental sessions. Secondly, participants did not undergo a specific familiarization session to become accustomed to viewing the repetition velocity displayed on the screen. However, they received prior instruction and became familiar with observing the repetition velocity during the warm-up routine, enabling them to learn how to utilize and interpret the visual feedback between repetitions (only in the visual feedback condition). This approach likely minimized the impact of not having a dedicated familiarization session on the study results.

Conclusion

Our findings demonstrate that both visual feedback and verbal encouragement conditions enabled athletes to increase velocity compared to the control condition with no feedback during a powerlifting session. This improvement can be attributed to factors such as motivation and a shift in focus.

Practical applications

The use of a device that measures and provides real-time visual velocity feedback for each repetition can have an impact on training sessions. By providing athletes with immediate feedback on their velocity performance, it facilitates a continuous improvement in average velocity throughout the training session. This, in turn, can positively influence the overall effectiveness of training, particularly for individuals who train without the presence of a training partner or coach.