1. Introduction

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Strength & conditioning practitioners endeavour to seek novel and practical methods to enhance athletic performance. The use of technology has become an integral part of strength & conditioning practice, kinematic (velocity) and kinetic (power) variables can be measured by commercially available devices[1,2]Monitoring repetition velocity during strength training provides the practitioner with valuable information regarding the neuromuscular demands and the training effect during that particular movement[3]. The use of instantaneous feedback (knowledge of performance & knowledge of results) can have a significant influence on athletic performance[4-9]. Recent research10demonstrated that when athletes were provided with visual kinematic information during a back squat, this led to the maintenance of barbell velocity in subsequent repetitions, enhanced motivation and competitiveness. However, little research has been conducted on the use of load deception to enhance weightlifting performance.

The concept of false feedback has gained traction within the community. For example, informing the athlete that they are lifting a lower weight than they are, the task is perceived as less challenging and leads to increased motivation[11,12]. Siff & Verkhoshansky[13] conceptualized the idea of weightlifting with an unknown load. They theorized that by implementing load deception, it would allow the athletes other senses to super-compensate and enhance performance during a lift. They also proposed that this enabled the athlete to remember joint angles, muscular tension, movement patterns and reproduce them more effectively. This deception has been theorized to enhance proprioceptive sensitivity and makes it possible for the athlete to make more internal visualisations of a technique[14]. One of the first studies on unknown loads was conducted by Ness & Patton[15] on bench press performance.

They found that there was significantly higher strength performance when the resistance was greater than the subject believed. However, the research failed to specify why this enhancement had occurred.

A recent study[16] on handball players established that the use of unknown loads in a bench throw increased power outputs and throwing velocities compared to known loads. The researchers suggest that the unknown load stimulated the central nervous system to overestimate the mass, causing a larger force production than was required to move the real mass. Furthermore, another study established that load deception led to greater adaptations in eccentric phase variables particularly under moderate-high loads in well trained athletes[17].This type of training stimulus may provide an innovative strategy for stimulating rapid muscle activation and enhanced force production[18].

Recently, the application of weightlifting exercises and their pulling derivatives have gained popularity amongst practitioners[19-22].These exercises rely on the application of large impulse over a short period of time during the second pull to create the displacement of the barbell at a rate sufficient to enable the lifter to catch the bar in the rack or overhead position[23-26].Their derivatives enable athletes to develop their ability to apply large enough impulses across different phases of the lifts. Furthermore, the quest to enhance rate of force development (RFD) remains elusive for practitioners. RFD is an adaptation which enhances muscle activation which results in greater force production in shorter time periods[27-29]. Researchers[30-32] suggests that RFD and PPO during lower body resistance exercises are developed across a range of loads. The capacity to produce maximal voluntary activation in the early phase of explosive contraction (first 50-75ms) seems to be a determining factor in enhanced RFD production[33]. Furthermore, Suchomel et al.,[34] advocates that optimal loads should be between 90-95% of 1RM for weightlifting derivatives. Theoretically, an increase in RFD allows for a higher level of muscular force in early phase of muscular contraction (0-200ms)[35]. Conclusively, athletes who possess the ability to produce dynamic explosive strength tend to have superior athletic qualities[36,37].

The second pull of the clean produces the most force during all the phases[38-41]. The second pull of a sub maximal clean can generate vertical velocity from ranges between 0.88m/s to 1.73m/s in elite weightlifters[42]. Kilduff et al.,[43] Hoffman et al.,[44]advocates the importance of high force, high velocity training program (weightlifting) to develop strength, speed and power for field-based athletes. These improve-ements were based on the higher RFD and improved contractile speeds associated with high force, high velocity movements. Conversely, research[45] discovered that the mid-thigh clean pull resulted in higher PPO compared to a power clean. Kipp et al.,[46] Suchomel et al.,[47]and Hori et al.,[48] suggest these derivatives from mid-thigh simulate joint angles which are performed during the drive phase of both running and jumping during athletic performance. Izquierdo et al.,[49] suggest that greater average and peak velocity, average force and average power output have been demonstrated by using training modalities that reduce the deceleration phase by allowing the load to be projected in a throw or jump.

A plethora of research has demonstrated that weightlifting pulling derivatives produce similar or greater force, velocity power variables during the second pull compared with full weightlifting movements.[50-52] Suchomel et al.,[53]andComfort et al.,[54] suggests that weightlifting pulling derivatives from blocks may require a greater RFD compared with a dynamic start because the athlete would have to overcome inertia. Furthermore, a more upright position during the pull phase could enhance force production capabilities[55]. The enhanced force production could improve mechanical advantage and stimulate a potentiated stretch-shortening cycle. The derivatives may also enable the practitioner to overload the triple extension movement, enhancing strength and power character-ristics[56,57]. Therefore, the application of these derivatives may enhance the triple extension movement within the athletic population[58-60]Also, from a pragmatic perspective, the teaching of derivatives may enable the athlete to achieve the ability to produce higher velocities and higher force movements without gaining full technical competency of the lift.

The objective of this research is to ascertain whether not knowing the load to be lifted during of a mid-thigh pull (MTP) could enhance kinetic and kinematic variables. The research analysed if an athlete provided a ‘true’ maximal effort when faced with a known load compared to an unknown load. It has been theorized that when the athlete is unaware of the load other senses will super-compensate and enhance performance.[13] The MTP offers a practical application that is easier for less experienced athletes to learn because of the omission of the catch phase.45 Furthermore, MTP produces the greatest lower body power as compared to other weightlifting derivatives[61,62]. The findings of this project may result in an opportunity for training adaptations for both weightlifters and sports performers who adopt derivative weightlifting movements[63-65]. Consequently, the stimulus of unknown load could provide a novel coaching application.

2. Methods

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2.1. Participants
The study was approved by the Cardiff Metropolitan University Institutional Ethics Committee, conforming to the declaration of Helsinki. All participants provided informed consent prior to participation. Fifteen male collegiate athletes (age 21.8 ± 2.3, height 171.8 ± 7.5cm, mass 89.3kg ± 9.8kg, MTP 1RM 135.5kg ± 18kg) participants were recruited from the Institutions Weightlifting Team and students who were proficient in weightlifting movements (GAA-Gaelic Football & Hurling, Rugby). All participants were engaged in a structured resistance training program for18 months and were participants in the institutions sport science support program. This was to ensure competency of skills involved in the study. The recruitment of participants was on a voluntary basis. Prior to the research, MTP familiarisation sessions were offered to the participants. All testing was completed in the Institutions high performance gym.

The participants were informed of the testing procedures and the risks associated with the protocol. All participants consented to partake in the study. Participants were asked to wear appropriate clothing and footwear. Prior to the test, participants were required to complete a physical activity readiness questionnaire (PAR- Q). Once all participants had consented and were eligible to participate in the study, the testing commenced. Participants were requested to refrain from strenuous exercise 48 hours before testing, maintain normal dietary intake and attend the testing in a hydrated state.

2.2. Testing
Anthropometric data (mass - Seca 875 Class (III)), (height - Seca 213 Height Measure) and 1 repetition maximum (1RM) of MTP was collected during the first test. The second session was for the specific testing of the unknown MTP at apercentage intensity 1RM randomly selected by the researcher. This involved the collection of velocity-based variables for further analysis which was measured by a Tendo Weightlifting Analyzer System (Trencin, Slovak Republic). Acceleration was analysed from variations in velocity over time [acceleration = velocity (v) / time (t)][66].An abundance of research concluded that muscular power can be measured with a high degree of reliability with this unit[67-70]Furthermore, Garnacho-Castaño et al., [71]demo-nstrated that Tendo Weightlifting Analyzer System was a reliable system for measuring movement velocity and estimating power in strength based exercises. There was a minimum of 48 hours between the two sessions to ensure optimal recovery after maximal testing in the first session[72].Both testing sessions were completed at the same time to ensure reliability.

Before both sessions, a dynamicwarm-up protocol was completed involving hip/glute activations, dynamic whole-body movements and potentiation jumping activities. This was followed by a dynamic complex barbell warm-up of the movements involving the MTP[73]. Finally, a 1RM protocol using the MTP as suggested by Baechle et al.,[74]was completed. The same warm up protocol was used prior to the testing of blinded MTP. The only difference was when the warm up was complete, the participants left the testing area while the weight was randomly selected by the researcher. The participant was then double blindfolded outside the gym and guided back into the power rack by the researcher. This was to ensure the participants avoided any trip hazards on returning to the test platform. After the blinded attempt, they were guided back out of the gym and the next load was randomly pre-selected. Participants performed five individual unknown MTP attempts whilst the barbell was connected to the Tendo Weightlifting Analyzer System to allow for analysis of several velocity based variables. The filter within the Tendo Weightlifting Analyzer System was set to 10Hz as recommended by Cronin et al.,[75]and McMaster et al.,[76]. The inclusion of body weight was used during testing as recommended by Cormie et al.,.[77] The load was randomised between 75%, 80%, 85% 90% and 95% of MTP 1RM. There was 6 minutes’ rest period between each repetition to prevent any potential potentiating or fatiguing effect.

The power rack was modified so the bar (Jordan, Norfolk, UK) was at the athlete’s mid-thigh height. Irrespective of stature, the preferred angles of the peak power position are approximately 60-70°, 120-130°, and 140-150° at the ankles, knees, and hip, respectively. [78,79]This was achieved by adapting the safety bars to the desirable height to achieve the angles of the jump position of the clean. The power rack could be adjusted within 5cm deviations. Participants feet were positioned shoulder width apart with the bar positioned at mid-thigh over the midfoot. Participants used the hook grip during MTP attempts. The participant contacted the barbell at a mid-thigh position. Participants adopted their MTP position and maintained tension throughout the upper body and a naturally concave curvature of the thoracic spine to maintain appropriate hip angle to maximise force produced through the floor. The ascending part of the lift was completed forcefully with triple extension through ankles, knees and hips. Participants shrugged shoulders and allowed the barbell to travel up along thighs. Elbows remained ‘long and locked’. On the descent phase of the lift, knees were flexed to absorb the load[80].

2.3. Data Analysis
The kinetic and kinematic variables AV, PV, AP and PP were calculated as follows: velocity (m.s1) = vertical movement of the bar (m) x time (s^-1), acceleration (m.s^-2) = vertical bar velocity (m.s^-1) x time (s.^-1). force (N) = system mass (kg) x vertical acceleration of the bar (m.s^-2) + acceleration due to gravity (m.s^-2) power (W) = vertical force (N) x vertical bar velocity m.s^-1).70 Regression equations were used to predict estimated velocity based measures from the 1RM using Excel software (Microsoft: Redmond, WA, USA). 81,82From the linear regression formula the load when velocity is zero and velocity when load is zero was calculated to estimate the various loads in AV, PV, AP and PP[81].

2.4. Statistical Analysis
Standard statistical methods were used for the calculation of descriptive statistics (means, standard deviations (SD)). The normality of the data was analysed by using a Shapiro-Wilk Test. A paired sample t-test was used to compare means and ensure the data was normally distributed with no outliers.[83]The alpha level was set at p ≤0.05. Relative reliability between repetitions within each testing session was determined using a 2-way random effects model intra-class correlation coefficients (ICCs) and 95% confidence intervals. The ICC r values was interpreted according using the criteria of Cortina84where r 0.80 is highly reliable[85,86]. Effect Size[87]classification was determined using Hopkins[88] scale which defines < 0.2, 0.2-0.6, 0.6-1.2, 1.2-2.0, 2.0-4.0 and >4.0 as trivial, small, moderate, large, very large and extremely large respectively[89,90]This type of magnitude statistic can enable the reader to infer whether this type of training stimulus has practical application in addition to statistical significance[91].All statistical procedures were analyzed using SPSS 24 (IBM, New York, NY, USA).

3. Results

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The ICC indicated that the dependent variables were reliable (AV; r=0.92, AP; r=0.89, PP; r=.090 and PV; r=0.93). Table 1 shows significant p-values for all known and unknown loads of the MTP. There was a significant difference between pre AV 75 (0.49 ± .11) and post AV75 (0.66 ± .097) conditions; t (14) =-5.66, p = 0.000 (ES = 1.66; large). There was also a significant difference between pre AV 80 (0.47 ± .097) and post AV 80 (0.60 ± .099) conditions; t (14)=-4.23, p = 0.001 (ES = 1.36; large). There was no significant difference between pre-AV 85, 90, 95 and post AV 85, 90, 95 (p-values ranging 0.023 to 0.129; ES ranging from 0.52 to 0.86; small to moderate).

Figure 1    Figure 2    Figure 3    Figure 4    Table 1

4. Discussion

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The objective of this study was to determine whether not knowing the load to be lifted during an MTP performance across a variety of randomised loads led to improvements in kinematic and kinetic variables. The research demonstrated that unknown loads at 75% 1RM led to significant changes in AP with small ES, In AV, there was a large ES and in PV there was a moderate ES. Furthermore, significant change occurred in AV unknown loads at 80% 1RM with large ES. There was no significant difference in AP, AV, PP and PV variables across 85, 90, 95% 1RM (trivial to small ES). It appears that these findings especially at loads between 75% and 80% 1RM lead to improved performance in velocity variables. Specifically, Kipp et al,[92] demonstrated that optimal external mechanical power output during a power clean was between 75% and 85% of 1RM. These findings also coincide with Sabido et al., who found that unknown loads lead to greater power outputs in early time intervals and increased throwing velocity during an unknown bench throw. Comfort et al.,[93] demonstrated that individual peak power occurred at ranges between 60% and 80% 1RM. Male collegiate athletes demonstrated significantly greater bar velocities with 40-80% 1RM during a known MTP performance[94]. This was of similar cohort used in this study. Cormie et al.,[95] further advocates that weightlifting loads ranging from 50% to 90% of 1RM have a significant effect in improving peak force, velocity and impulse. However, Haff et al.,[96] proposes in a known clean pull loads of 80% 1RM or less produces the highest power outputs, which supports the results in this study. Furthermore, this study coincides with Jidovtseff et al.,[97] who advocated that loads between 54 and 84% of 1RM should be used to emphasize power production when using load-velocity relationships. Jandačka and Beremlijski[98] demonstrated that the optimal load for reaching maximum power output for dynamic strength effort was between 50 to 80% of 1RM in athletes. Training with optimal load is important due to the neural factors which could contribute to enhanced motor-unit recruitment, rate-coding and synchronization. The higher threshold Type II muscle motor units are recruited during higher power outputs[99] Conclusively, this can allow practitioners to infer that these loads replicate the strength-speed segment of the force-velocity curve which occurs between 0.75-1.0m/s[100,101].

To the best of the researcher’s knowledge this is the first study which used an weightlifting derivative at unknown loads. The study attempted to demonstrate that, when an athlete is aware of the load, they do not produce maximal effort (kinematic and kinetic variables). Conversely, when faced with an unknown load, they produce increased effort which manifests itself in increased kinematic and kinetic measures. This seemed to be the case in study at 75% 1RM and to a certain extent at 80% 1RM. It has been theorized that mechanism of unknown loads stimulates the central nervous system to overestimate the weight, thus allowing a larger force production to move the actual weight[102].Hernández-Davóet al. hypothesize the potential mechanisms used during an unknown load involve changes in both voluntary activation and reflex-mediated muscular activation. Furthermore, unknown loads have been associated with increased stiffness and greater recoil of the muscular- tendon unit which are associated with concentric performance during SSC activities[103].

The over-estimation of load may be due to muscle pre-activation which is often used as a mechanism to increase joint stiffness[104]. The mechanisms of pre-activation allow the muscular-tendon unit to produce a higher muscular force at the concentric element and could have enhanced unknown loads at 75% 1RM in AV, AP and PV. Furthermore, the co-activation in the agonist muscle-tendon unit can enable elastic energy to be stored and potentially used in the concentric phase of the movement. This will produce superior rapid force during the primary phases of the unknown MTP[105].It has also been suggested that co-activations increase joint stability and stiffness[106].The movement velocity could have led to improvements in the performance characteristics during the unknown MTP loads. This type of stimulus has been proven to enhance the reflex inhibition of the Golgi tendon organs and the facilitation of the muscle spindles. Additionally, this can stimulate synergistic activation of antagonist and agonist motor units[107,108]. The use of unknown loads could elicit enhanced neural contributions which lead to higher-power outputs including motor- unit recruitment, rate coding and synchronization in known loads[99].

The method of using unknown loads may provide an important stimulus for the increased activation and subsequent movement velocities during weightlifting movements[109].This type of stimulus can enable practitioners to utilize weightlifting pulling derivatives to stimulate the required adaptation.110Additionally, if one can perform repetitions at higher movement velocities, this may stimulate dynamic muscular strength adaptations at loads between 60-79% 1RM.[111]In conjunction with this research, loads between 75%-80% led to significant p-values and moderate to large effect sizes in average power and peak velocity. The use of unknown loads could enable practitioners to utilize strength-speed training phase more effectively, which in turn allow further increases in RFD, power and maintenance of strength levels[112,113].Recent research demonstrated that moderate to heavy loads (65-80% 1RM) optimized power output during weightlifting derivatives[114]The modality of explosive strength training provides an effective stimulus for improving early phase (0-100ms) explosive force[115].Consequently, the use of unknown loads could have positive implications in physical rehabilitation settings and return to previous performance protocols[116].

This research also provides further evidence that the weightlifting derivative of the MTP can be used as a method to increase performance variables such as peak force, velocity and impulse[117]. Additionally, because the unknown load occurred from a static start (on safety bars in this study) this may require a greater RFD due to the fact that the athlete would have to overcome inertia of the load. The MTP is a ballistic movement that causes vertical thrust with enhanced speed and force production in a minimal timeframe. A practical benefit of using weightlifting pulling derivatives such as the MTP is the reduced technical demand which potentially makes it easier for the athlete to learn. It may also reduce the potential for injury to the wrists and shoulders due to the elimination of the catch phase[118].Furthermore, during intense periods of training, the catch phase may be eliminated to ensure the athlete is not being over-stressed in terms of training load. By eliminating the catch phase, it can allow the athlete to focus on completion of the triple extension. This can potentially overload the triple extension that is specific to the movement demands of the sport. De Weese et al,[119] suggest that weightlifting derivatives can be programmed during specific training phases to coincide with speed development phases. In particular, the MTP could be used in the strength-speed phase to compliment the maximum velocity sprinting phase. Furthermore, one can overload the second pull phase considerably compared to the full weightlifting movement[45,120,12]

A major limitation of this study was the use of estimated loads to determine the load of the unknown MTP 1RM. In the future, this could be determined by clean or power clean 1RM and applied to determine the MTP specific loads as used by Comfort et al., A further limitation was the relative inexperience of the subjects used. In future studies, it would be appropriate to examine the effect of unknown loads on athletes who have superior training ages and to apply more liberal effect sizes for elite populations. Also, the regression analysis used to estimate velocity variables at various 1RM’s has recently been questioned by Banyard et al.,[122] who reported a large variability in velocity 1RM. However, Carroll et al.,[123] discovered that there was a significantly strong relationship between mean concentric velocity and relative intensity. Future research could determine a load-velocity relationship for the MTP to predict 1RM. Potential research could also be conducted longitudinally to determine the effect of unknown loads across a training cycle. The rest periods used between the randomised loads may not have been sufficient and could have had a fatiguing effect on subsequent repetitions. This is a potential explanation for the insignificant differences at 85%, 90%, 95% unknown 1RM. Additionally, the researchers observed that the participants seemed apprehensive on the first attempt of their blinded MTP effort, which could have affected the performance outcome. However, once the athlete adjusted to being blindfolded, they seemed to become more comfortable to the stimulus. In the future, a pre-trial blinded attempt could be used to overcome this potential anxiety.

5. Conclusion

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This study demonstrated that when the load was not known participants were able to displace it at significantly greater peak and mean velocities, which resulted in significantly greater mean power. The results of this study suggest when load was not known between 75% and 80% 1RM MTP lead to greater performance in velocity based variables compared with known loads. Furthermore, the use of unknown loads seems to offer a novel stimulus to the central nervous system which leads to improvements in specific performance in a weightlifting pulling derivative. This is important for sports performance where the expression of critical intensity’124 is an extremely desirable characteristic. This type of training stimulus may allow practitioners to provide an acute strength-speed application to training interventions. Further research is necessary to determine whether further exposure to training with unknown loads would lead to enhanced improvements in velocity variables compared to tradition strength training methods. Secondary, the use of weightlifting pulling derivatives appears to be an important method to train sports specific adaptations. However, practitioners need to be cognizant that unknown load derivatives are another method to include in the spectrum of training modalities and therefore used when deemed appropriate and necessary.

Acknowledgment

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This manuscript is original and has not been previously published, nor is it being considered elsewhere until a decision is made on its acceptability by the ARC JRSM Editorial Review Board. The author would also like to thank the participants for their time and efforts during in the study.

Declaration of Conflicting Interests

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The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

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