Introduction

The sport of weightlifting contests two lifts - the snatch and the clean and jerk. In the snatch (Figure 1) the bar is pulled overhead in one movement; generally the lifter will squat under the bar when catching it overhead. After catching the bar overhead the athlete stands erect, with the feet parallel. In the clean (Figure 2a) the bar is pulled to the shoulders. As with the snatch, the lifter can split or squat under the bar, when catching it on the shoulders - the lifter then stands erect. After standing erect the lifter dips (by flexion at the knee) then drives (i.e. jerks) the bar overhead using hip and knee extension and either splits or squats under the bar as it is caught overhead on extended arms. The lifter then stands erect (Figure 2b).

Figure 1: Snatch
Technique Analysis - Rezezadeh Hossein IRI, +105kg, Snatch -206kg

Figure 2a: Clean
Technique Analysis - Maiyuan Ding CHN, +75kg, Clean 157,5kg

Weightlifting movements and particularly pulling movements have become integral parts of the training programmes of many different sports. These explosive movements can have great transfer of training effect provided reasonable exercise technique is used. The purpose of this discussion is to: first describe the proper technique used in the pulling portion of the snatch and clean, second examine the potential importance of these lifts for sport and third to examine the potential outcome of training in a similar manner as weightlifters.

Snatch Versus The Clean

First it should be noted that the term pull is really a misnomer. Although the term pull is used, it is actually a push into the floor by the leg and hip extensors, which propel the bar upward. However, by convention the term "pull" is used worldwide.

There is little difference in the basic pulling technique for the snatch and clean. The most efficient pulling method for both the snatch and clean is referred to as the "double knee bend" and will be discussed in detail later. In the snatch the grip is relatively wide (Figure 1) which facilitates catching the bar overhead and reduces the height to which the bar must be pulled before fixation. In the clean (Figure 2a) the grip is relatively narrow compared to the snatch, which facilitates catching the bar on the shoulders. For the snatch (compared to the clean) the differences in hand spacing may result in, a lower hip placement at lift off, changes in the point of bar contact on the thigh and results in somewhat different stresses on the musculature, particularly the shoulder girdle.

Basic pulling sequence

The basic pulling technique can be described as follows:

If the arms are not straight and the back is not flat or arched forming a semi-rigid link system, then forces cannot be transmitted efficiently from the leg and hip extensors to the bar.

Lift-off (Figures 1 and 2a - position 1)

Bar at knees (Figures 1 and 2a - position 2)

The lifter bar complex has moved upward and back completing the "first pull".

Bar at mid thigh (Figures 1 and 2a - position 3)

A "transition" from the bar at the knee until the mid-thigh position, results from a forward movement and/or re-bending of the knees such that an un-weighting effect occurs. The forward movement/re-bending of the knees is typically referred to as the "double knee bend" (DKB), the first knee bend occurring at the initiation of the lift. The DKB is largely a result of the backward-upward movement of the trunk during the transition, which contributes to a fixation or more typically a forward movement of the knees. Re-bending of the knees is often as great as 10-20° (Bartonietz 1996, Roman and Treskov 1983). Although not intentional, there is usually a decrease or plateau in bar velocity during this transition as the knees are re-bent and the body is re-aligned for greater vertical force production (Bartonietz, 1996, Enoka 1979, Garhammer and Gregor 1992). A marked drop in bar velocity could be a result of the lifter starting the bar off the floor too rapidly by raising the hips too fast or as a result of weak hip extensors (Bartonietz 1996). It is critical that the DKB take place rapidly as this will reduce the drop in velocity during un-weighting and enhances the efficiency of the re-alignment as a result of a stretch-shortening effect (Bobbert et al. 1996, Enoka 1979, Kuahanen et al. 1984, Reiser et al. 1996).

The second pull can be effectively initiated from this position. This mid-thigh position is crucial for effective lifting, as it is the position, which allows the highest maximum force and rate of force production to be achieved.

Second pull (Figures 1 and 2a - position 4)

During the second pull, peak force, rate of force development, power and bar velocity are at their highest values. It should be noted that the duration of the second pull is negatively correlated with the efficiency and success of a lift (Kuahanen et al 1984), thus, explosiveness is a primary consideration.

Foot centre of pressure

Lift-Off Knee Mid-Thigh Shoulder Shrug - Plantar Flexion

Vertical force

Use of a force plate will also allow the measurement of vertical ground reaction forces. It should be remembered that the "pulling" movements are actually a push into the ground. This force, largely created by the leg and hip extensors, is transmitted through a semi-rigid link system consisting of the mid-section, trunk and arms to the bar.

As can be observed in Figure 4, (1-2) the first pull in which the bar moves from the floor to just above the knees is characterised by an initial rise in force followed by a relatively steady force output. During the transition (2-3) there is an un-weighting phase as the knees are re-bent. During the 2nd pull (3-4) there is a sharp increase in force until the lifter drops under the bar for the catch. Even at maximum weights the entire lift should be completed in about 1 second or less.

Elite lifters will typically complete the transition phase quicker than un-skilled lifters. A faster transition (double knee bend) among skilled lifters likely results from the ability to apply eccentric force at faster rates or by applying force at greater magnitudes (Kauhanen et al. 1984). Furthermore, the elite skilled lifter can accelerate the bar faster during the subsequent concentric phase. In analysing (both qualitative and quantitative) over 1000 lifts from national (USA and British) and international contests it is quite clear that the majority of high calibre and elite lifters (99% +) placing in the top 5 of these contests use a double knee bend pulling technique.

Most elite lifters use a rather pronounced "double knee bend" or stretch shortening during the transition, with a final knee angle of about 130-140°, the final knee angle in the snatch typically being somewhat smaller (greater knee bend) then in the clean (Bartonietz 1996, Reiser et al. 1996). Some elite lifters use a much shallower double knee bend with greater final knee angles. It is not completely known why this difference occurs; however, it may be due to differences in elastic properties or muscle activation abilities. Interestingly, the authors have observed that a shallower DNB/SSC tends to be characteristic of lifters in lighter classes, particularly in the clean (< 85 kg).

Vertical force - Straight pull

The vertical forces resulting from a double knee bend technique can be contrasted with a straight pull in which there is no double knee bend and often there is considerable arm pull. Using data from our laboratory (Figure 5) it can be noted that the greatest forces occur shortly after lift-off and the force often decreases markedly thereafter. This type of pull results in smaller magnitudes of peak force and peak rate of force development and often takes a longer to complete, thus reducing the effectiveness of the pulling movement.

Figure 5

Sequence of a clean

In this sequence (Figure 6) of the clean we can clearly observe the double knee bend occurring. The various positions previously discussed can be noted in this series of photos. Position 1 corresponds to lift-off at which the centre of foot pressure is forward near the ball of the foot. At position 2 the bar has moved to the knees and the centre of pressure has moved toward the heel. Position 3 corresponds to the double knee bend position at which the bar has moved to the mid-thigh, the knee angle here will be about 130-140° and the trunk is nearly vertical. This position is the strongest of the entire pulling sequence and is crucial for high-level success. In position 4 we can observe complete extension after which the lifter moves under the bar.

Sequence of a snatch

This sequence (Figure 7) depicts a snatch. Note that the positions attained during the pull are similar to those attained during the pull for the clean. Some differences occur as a result of hand spacing. For example in the double knee phase the bar would touch the lifters upper thigh rather than mid-thigh.

It is important that the bar does actually touch the thigh during the double knee bend. This is because leaving the bar in front of the thigh creates a position from which less force can be exerted. Furthermore, the further the bar is in front of the lifterÕs centre of mass, then extra energy must be expended in order to bring the bar back in line so that it can be successfully caught on the shoulders or overhead. While brushing the thigh (not a drag or bang) may increase the friction encountered during the pull - this is more than offset by the ability to accelerate the bar from the DKB position.

Squat snatch bar trajectory (Figure 8)

The vertical and horizontal displacement of the bar forward and back can be seen by observing the bar from one end. This (Figure 8) was generated from data collected using a V-scope (Lipmann Electronics, Wingate Israel). The V-scope is an instrument that uses an ultra-sound/infra-red technology, which allows accurate tracking of the bar path. In this view of a snatch, the lifter would be facing to the right. Note that during the pull to the upper thigh that both the bar and lifter would move up and back.

As the 2nd pull is initiated the bar moves away from the lifter because it brushes the thigh and also because the lifter moves to the balls of the feet at the end of the 2nd pull After complete extension the lifter moves under the bar and catches it overhead. Figure 9 is a tracing of the bar path of a squat snatch in which the lifter descends into a full squat position when catching the bar overhead. In a "power snatch" the weight is pulled high enough so that a squat under the bar is not necessary and the bar is caught overhead with the tops of the thighs above parallel. Compared to a power snatch, note that the bar travels a shorter distance vertically, due to the weight of the bar, and also travels further downward as the lifter catches the bar in a full squatting position.

Peak force occurs just after the initial thigh contact and peak velocity shortly after peak force; peak power typically occurs in between peak force and peak velocity.

Squat clean bar trajectory

Figure 10 shows the bar trajectory of a squat clean. Because of the difference in the weight of the bar and the resulting velocity, a heavy clean will not be pulled as high as a snatch.

Power clean bar trajectory

If the catch were made with the thighs above parallel it is termed a "power snatch or power clean". Power snatches and cleans can be performed with light to moderately heavy weights. The higher velocities achieved during power movements will allow the catch for the snatch or clean to be made without descending into a complete squatting position. Figures 11a and 11b show the typical receiving position for a squat snatch and a squat clean.

Figure 11a	Figure 11b

Hang clean bar trajectory

In many sports hang snatches, cleans or pulling movements are used on a regular basis (Bartonietz 1996, Bartonietz 2000). The term "from the hang" typically means that the movement is initiated from a standing position with a preliminary dip before initiating the upward phase of a pull. The hang can be achieved from a variety of positions, the most common are from the thigh or from the knee. This (Figure 12) shows the bar trajectory of a hang snatch beginning at the waist. The initial very quick downward movement (bending of the knee) provides a brief stretch shortening cycle that can enhance the upward force production.

Good technique is essential for a number of reasons including:

• transmitting forces efficiently and in the appropriate direction so that ultimately a greater weight can be lifted,
• the potential for carry-over to other sports performances will be enhanced and
• the potential for injury can be reduced.