(Nejadian et al., 2010)
The B trajectory is considered to be the ideal trajectory (Liu et al., 2018; Stone et al., 2013). This trajectory is the most common trajectory seen in elite lifters (Liu et al., 2018; Akkus, 2012; Gourgoulis et al., 2000; Isaka et al., 1996; Musser et al., 2014). Further, a backwards barbell trajectory (B) decreases the distance the barbell is away from the body (Chen & Chiu, 2011). Interestingly, anthropometry of a lifter and barbell displacement are related (Musser et al., 2014). Athletes with longer legs relative to their trunk more commonly pull with an A trajectory, where the bar path crosses the vertical reference line during the turnover (Musser et al., 2014). Athletes with longer trunks relative to their legs more commonly pull with a B trajectory where the bar path never crosses the vertical reference line (Musser et al., 2014). In the first pull, thebar should move toward the lifter (Gourgoulis et al., 2009). In both the A & B trajectories the bar moves toward the lifter, but not in the C trajectory. This is the reason the C trajectory is considered an ineffective trajectory (Gourgoulis et al., 2009;Musser et al., 2014). With all trajectory types, it is best when the lifter’s barbell path is close to the vertical reference line with a small change in trajectory in the catch phase. This makes the chance of success is higher (Lin et al., 2015).
Displacement
During the first pull and transition elite weightlifters pull the bar towards themselves creating posterior displacement. This is controlled during the second pull by the anterior acceleration created by the hip extensors (Isaka et al., 1996). The explosive power created by the hip extensors in the second pull moves the body backwards. This application of force produces a small amount of horizontal barbell travel which is necessary for optimal application of force (Isaka et al., 1996). Therefore, horizontal barbell displacement is the result of effective power application and a characteristic of good technique (Korkmaz & Harbili, 2016; Isaka et al., 1996). In some cases, this horizontal barbell displacement from the second pull can be too great, and controlling the barbell becomes difficult in the catch (Korkmaz & Harbili, 2016). As skill level increases, horizontal barbell displacement decreases (Korkmaz & Harbili, 2016). In fact, the amount of barbell displacement in the turnover for elite weightlifters is less than half of the amount for non-elite (Valentin et al., 2020). In the turnover phase, barbell displacement created by the hip extensors in the second pull is 3.4-4.8% for the snatch and 9.8-11.8% for the clean of elite weightlifters (Valentin et al., 2020). The small barbell displacement percentages for elite lifters, along with the fact that non-elite lifters have values that are over double, makes it clear that very little horizontal displacement is optimal. In fact, small amounts of horizontal barbell displacement are characteristic of better weightlifting technique (Liu et al., 2018; Nagao et al., 2019;Gourgoulis et al., 2009). Along with minimizing horizontal displacement it is also important to keep the bar close to the body throughout the pull. When the barbell is farther away from the lifter during the transition, or at the point of maximal height, the bar is harder to stabilize in the catch phase (Chiu, 2011). Further, the greater distance the barbell is away from the body at the point of maximal height, the more likely it is to be lost behind (Chiu & Liang, 2010). Another factor during the turnover is minimizing the amount barbell drop before it is stabilized. The measurement of barbell drop can be used to determine success in the snatch (Nagao et al., 2019). For optimal technique, the amount of drop distance in the catch phase should be minimal (Lin et al., 2015; Nagao et al., 2019).
Velocity
The ideal pull should have a smooth increase in velocity with a single peak in velocity (Liu et al., 2018; Harbili, 2012; Gourgoulis et al., 2009). The presence of multiple velocity peaks in the pull, indicates ineffective technique (Gourgoulis et al., 2009). This peak in vertical velocity should occur at the end of the second pull (Sandau & Granacher, 2020; Isaka et al., 1996). The first pull has a large effect on the maximal velocity reached at the end of the second pull and as a result the amount lifted (Sanau & Granacher, 2020). As the load increases, the velocity lost at the end of the second pull is mostly due to velocity lost in the first pull (Sanau & Granacher, 2020). Higher level weightlifters have a greater vertical velocity at the end of the first pull (Campos et al., 2006). During the transition, losses in vertical velocity should be minimized to prevent negative momentum of the barbell (Harbili & Alptekin, 2014). Also, the transition from first pull to second pull should be fast and include a small bending of the knees for best technique (Gourgoulis et al., 2009). This action stores elastic energy in the knee extensors which will add to the explosiveness of the second pull (Gourgoulis et al., 2009). In fact, Better lifters have greater vertical velocity at the end of the first pull (Campos et al., 2006). A decrease in acceleration during the transition should be discouraged and is a characteristic of inferior and flawed technique (Kipp & Harris, 2015;Sandau & Granacher, 2020; Gourgoulis et al., 2000). During the second pull the goal is a continual increase in velocity, with small acceleration peaks for optimal technique (Kipp & Harris, 2015). At the completion of the second pull, maximum vertical velocity should occur (Sandau & Granacher, 2020). But trying for maximal acceleration, in the second pull wastes strength that could be used to lift a heavier load (Kipp & Harris, 2015). In fact, elite lifters take longer to complete the second pull when compared to non-elite weightlifters (Liu et al., 2018). This allows for a longer time period to exert force on the barbell and, as a result, added vertical barbell height (Liu et al., 2018).During the second pull, the hip extensors velocity is greater than the knee extensor’s and this adds acceleration to the barbell, making the second pull explosive (Gourgoulis et al., 2009; Liu et al., 2018). A decrease in hip velocity will affect the explosive power needed in the second pull (Harbili & Alptekin, 2014). Also, an explosive plantar flexion accounts for up to 10% of the maximum barbell velocity (Gourgoulis et al., 2000). Therefore, explosive strength of the hip and ankle extensors is very important for a successful second pull phase (Harbili & Alptekin, 2014). The bar must also have enough velocity to allow for lifters to have enough time to move under the bar (Sandau & Granacher, 2020). This minimum velocity value required for a successful lift is called threshold velocity (Sandau & Granacher, 2020). The maximal height to snatch ranges from 71-77% of a weightlifter’s height with taller weightlifters needing to reach a higher percentage of their height (Ai et al., 2018). For the clean, the bar must be pulled to 60% of the weightlifter’s height (Ai et al., 2018). These values are for elite weightlifters and the less skilled would need to pull the bar to a greater percentage of their height for a successful lift (Ai et al., 2018).
Characteristics of different phases
The first pull is dependent on maximal strength and the second pull is dependent on explosive strength (Akkus, 2012; Sandau & Granacher, 2020; Harbili & Alptekin, 2014). Improving maximal strength of the hip and knee extensors is important for improving the first pull (Harbili & Alptekin, 2014). The use of snatch deadlifts and other exercises that target the knee and hip extensors is recommended (Sandau & Granacher, 2020). The second pull is dependent on explosive strength of the hip and ankle extensors (Harbili & Alptekin, 2014). Exercises such as snatch high pulls with intensities between 90-100% of snatch maximum are beneficial for improving explosive strength in the second pull (Sandau & Granacher, 2020). The direction of the first pull, amount of knee extension, and speed of transition are all important factors. Starting the lift properly is important because the direction of the first pull can determine the success of the lift (Gourgoulis et al., 2009). In the first pull, the bar should move toward the lifter (Gourgoulis et al., 2009). The foot pressure starts in the forefoot area and moves backwards in the first pull to the center of the foot as the barbell moves toward the lifter (Liu & Chen, 2001).During the first pull the hip angle should be maintained and the knee extensors should extend at a faster rate than the hip extensors (Mastalerz et al., 2019). Greater knee extension angles in the first pull facilitates a more explosive second pull by improving body positions to create more stored elastic energy in the transition (Akkus, 2012). The key is that this transition is rapid enough to store elastic energy and elicit a stretch reflex (Akkus, 2012). During the double knee bend in the transition phase, the center of pressure moves forward to the forefoot area (Liu & Chen, 2001). The proper sequencing of hip, ankle, knee and trunk extension is key for maximal vertical height (Campos et al., 2006). In the second pull the hip extensor’s velocity is greater than the knee extensor’s and this adds acceleration to the barbell, making the second pull explosive (Gourgoulis et al., 2009; Liu et al., 2018). A decrease in hip velocity will affect the explosive power needed in the second pull (Harbili & Alptekin, 2014). The forefoot pressure created by the double knee bend allows for a powerful plantar flexion at the end of the second pull, which can contribute up to 10% of maximum barbell velocity (Liu & Chen, 2001; Gourgoulis et al., 2000). Therefore, explosive strength of the hip and ankle extensors is very important for a successful second pull phase (Harbili & Alptekin, 2014)