Below is a great article from the latest issue of the Journal of Strength and Conditioning Research from Loren Chiu and his research group at the University of Alberta. This is very important as most only focus on the concentric explosive triple extension, but must remember that Olympic lifts also teach us to resist triple flexion.
Many sports, such as basketball and volleyball, include jumping activities. Jumping involves 3 general phases: (a) propulsion, (b) flight, and (c) landing. The landing phase is also described as the impact phase, as it involves a collision between the falling body and the ground. At impact, the body possesses kinetic energy as a result of the conservation of energy from the initial drop height potential energy. After impact, work is performed using eccentric muscle loading to absorb this kinetic energy (Devita and Skelly, 1992; Fry et al., 2003).
Previous research found the technique used to land from a jump influences the work performed at the hip, knee, and ankle. Bobbert et al., (1987) compared the impact phase of bounce and countermovement drop jumps, where bounce drop jumps had less ankle dorsiflexion and knee flexion than countermovement drop jumps. In bounce drop jumps, more work was performed at the ankle, whereas in countermovement drop jumps, work performed at the knee was greater. Similarly, Devita et al. (12) compared landings with greater and less than 90-degree angle of knee flexion. Landings with greater knee flexion required more work to be performed at the knee.
Impact is not unique to landing from a jump. Movements in the sport of weightlifting also involve propulsion, flight, and impact phases. In weightlifting, impact is a result of (a) the feet returning to the ground after a momentary separation and (b) receiving the barbell on the shoulders (i.e. clean) or overhead (i.e. snatch) which occurs when the feet contact the ground (8). Similar to landing from a jump, eccentric muscle loading is required to perform work and absorb energy present at impact during weightlifting.
Ten women athletes (volleyball and weightlifting) participated in the investigation. Athletes were involved in the following: (a) sports with jumping activities and (b) strength and conditioning training involving weightlifting exercises. All participants had been taught to perform the clean and power clean by a certified weightlifting coach. Further, they had a minimum of 6 months experience performing these exercises under the supervision of the coach.
Participants completed 2 sessions, spaced approximately 1 week apart. During the first session, maximal countermovement jump height was determined. Jump height was used to determine the height of the drop landing. Drop landings were performed by standing on a box adjusted to the maximum jump height, stepping off the box, and landing on 2 feet. Participants watched an instructional video followed by performing 5 jump and five drop landing trials. The video instructed participants to do the following:
- Land with feet symmetrical
- Land with knees and ankles bent
- Land with feet flat
- Land with the body upright; avoid leaning forward
- Absorb the landing using muscle tension
In the second session, participants performed jump and drop landings, power cleans, and cleans while data were collected using 3D motion capture techniques. Participants performed 4 repetitions of maximal effort block jumps with landings, followed by 4 repetitions of drop landings from a height equal to their previously determined maximum vertical jump height. Power clean and clean exercises were performed with a barbell load of 80% of the participant’s 1RM clean. Three sets of 2 repetitions were performed for each of the power clean and clean. Sets of power cleans and cleans were alternated to prevent an ordering effect.
Work performed at the hip, knee, and ankle were calculated during the landing and receiving phases of jumping and weightlifting tasks, respectively. Additionally, segment and joint kinematics and net joint moments were determined.
The most lower extremity work was performed in the clean and drop landing, followed by landing from a jump, and the least work was performed in the power clean (p < 0.05). For all tasks, work performed by the knee extensors was the greatest contributor to lower extremity work. Knee extensor net joint moment was greater in the power clean than jump and drop landings, and greater in the clean than all other tasks (p < 0.05). Knee flexion angle was not different between the power clean and jump landing (p > 0.05) but greater in the drop landing and clean (p < 0.05).
To absorb the kinetic energy present at contact, work must be performed ideally by muscles. If muscles are not able to perform work, energy may be absorbed by connective tissue, including ligaments and bones, which may result in injury (Mills et al., 2009). To absorb energy in landing activities, strength of the knee extensors is critical. Weightlifting tasks share similar biomechanics to landing from a jump but require greater knee extensor effort. Thus, the power clean and clean may be used to develop knee extensor strength appropriate for landing from a jump. In particular, the clean requires greater knee extensor loading than the power clean, which is a similar comparison to the knee extensor loading in full versus partial squat exercise (Bryanton et al., 2012). Weightlifting exercises such as the snatch, clean, and variations of these lifts are commonly used in strength training programs; however, there is an emphasis on the propulsion or pulling phase (Chiu and Schilling, 2005). The present research finds that there are benefits to receiving the barbell in weightlifting exercises, especially in the deep squat position. Strength and conditioning professionals should be aware of the benefits of weightlifting exercises such as the clean and snatch performed through a full range of motion. Athletes in sports involving impact activities, such as jumping and landing, should incorporate the clean exercise to develop the strength and flexibility required to absorb energies during impact.
Moolyk, AN, Carey, JP, and Chiu, LZF. Characteristics of lower extremity work during the impact phase of jumping and weightlifting. J Strength Cond Res 27(12): 3225– 3232, 2013