Strength training develops the muscles’ ability to exert force, for example pushing a heavy object. Power training develops the ability to exert this force in less time – ie to make the movement quicker, for example throwing a ball.
Sprinters can generate forces of up to three and half times their body weight when racing, so having sufficient leg strength to generate this force without injury is necessary (2). This explains the commonly quoted guideline that a power athlete needs to be able to squat a weight equivalent to twice their body weight – eg an 80kg male rugby player should be able to squat 160kg.
The squat and squat jump are two exercises that have a major role in developing leg strength and power. This article will look at research on squat variations and the squat jump and give some guidelines on what loads should be lifted in order to gain the greatest benefit.
Strength before power
The squat exercise uses most of the major muscle groups in the lower body, overlapping with those used in running and jumping, so it is very suited to most sports. The squat can increase the ability to produce power in the long term, but it has also been shown to improve power production in the shorter term through the post activation potentiation (PAP) effect in trained individuals (3,4).Post activation potentiation has not been fully explained yet, but the effects are the basis behind the theory of complex training, which combines strength and power exercises into small sets, where the muscles’ ability to produce a more powerful contraction is improved by performing strength exercises shortly beforehand.
However, this does not appear to happen in untrained individuals, who are simply fatigued from the preceding strength exercises (see this author’s article in PP198, June 2004). The assumption, therefore, in the rest of this article is that the athlete has already established a strength base (the ability to squat a load equivalent to their own body weight).
Chain squats
Although most squatting is performed using a simple barbell and weight arrangement, there are variations on this theme. A popular variation of the squat in the USA is to add chains to either end of the barbell.The chain is attached to the top of the barbell, with some portion of it on the floor. As the squatter descends, more of the chain is on the floor, decreasing the overall load. As the squatter ascends, less of the chain is on the floor, increasing the overall load. This arrangement requires greater force production at the top end of the squat (because more of the chain is off the floor and thus suspended from the barbell) when the legs are in a more mechanically advantageous position to produce greater force.
This mechanical advantage arises from the fact that the length of the quadriceps is shortened, allowing more opportunity for cross-bridge contractile activity.
At the bottom of the squat, when the quadriceps muscles are lengthened, there is less cross-bridge activation and the legs are at a mechanical disadvantage. So, although the external resistance is constant (the barbell), the force produced by the muscles isn’t constant due to mechanical changes.
The theory behind the use of chains is that it overcomes mechanical changes and produces a constant force throughout the movement. This may be of use in movements such as a lock forward scrummaging in rugby union, where more force may have to be produced with the legs nearly straightened in order to assist the prop’s push forward against the opposition.
An alternative method is to use elastic bands or tubing, with one end fixed to the floor and the other to the barbell. Again, as the squatter descends less resistance is produced because the tension in the elastic is reduced, but more resistance is produced on the ascent due to the elastic lengthening and tensing.
How big a chain? Well, it depends on the strength of the athlete! Chains can normally be bought in inches (width) and feet (length), with half-inch chains being a good size for strong athletes when squatting. Smaller chains can be used for intermediate athletes and also for the bench press.
A half-inch chain weighs around 7.5kg per foot. If the barbell rests on a typical athlete’s shoulder at 5ft off the ground, two half-inch chains would provide an additional 75kg of load. Descending 2ft would reduce this load by 30kg (2ft length of chain that was previously suspended would now be on the floor at each end of the barbell). So an athlete with these chains could have a barbell weighing 60kg, and be squatting 135kg at the top of the movement but only 105kg at the bottom.
Another proposed benefit of chain squats is that the athlete does not have to slow down their movement near the top of the squat; instead they still have to keep trying to move quickly to overcome the added resistance. This type of training movement is probably more appropriate for sporting situations where contact is involved, and the player has to drive into the opponent with maximum extension of the legs, rather than slowing down just before impact.
Chain squat research
Two studies have been conducted to test the efficacy of this training method. In the first, US researchers from Marquette University in Wisconsin looked at 11 college athletes and measured electromyographical activity during a squat with barbells, with barbells and chains, and with barbells and elastic bands (5).No difference was found in force production between the three conditions. However, the authors commented on the fact that all the athletes ‘felt’ the squats were different to perform. They also commented on the fact that part of the study design was to reduce the load of the barbell by 10% to accommodate either the chains or elastic bands. However, in normal training conditions, one of the advantages of using chains and bands is that additional loads can be lifted. This additional load may result in greater force production and therefore strength gains.
In the second study, researchers looked at 10 resistance trained adults and the effects of altering resistance at around 60% and 85% 1RM (maximum weight that can be lifted for one rep) of the squat(6). They used bands to provide an extra 20% or 35% of the total resistance and compared this to a controlgroup who were just doing the squat.
No differences were found in the rate of force development between the squat with bands and the squat without. However, both peak power and peak force were found to be greater when using bands. The difference was even more significant when performing the 85% 1RM, heavier load. The optimal condition appeared to be the heavier 1RM load, with 20% of the resistance coming from the bands. More research is warranted in this area, but the use of chains or bands in squats could be a worthwhile addition to athletes’ strength training routines.
Squat jumps
One method of developing power in the legs is through the use of weightlifting exercises such as the clean and the snatch. This is currently in vogue; with many national governing bodies (NGBs) issuing guidelines that all their funded athletes become proficient in these lifts.However, the time and effort that it would be necessary to invest in developing the technical proficiency in these lifts to allow the athlete to lift loads that develop power, may be better spent in performing other exercises that have similar benefits, but require less coaching – the squat jump being one such exercise.
How much load should be placed on the athlete? Well, the assumption made here is that they have already established a strength base (non-strength trained subjects respond differently to the squat jump than trained individuals, with loads as little as 5kg creating a decrease in peak instantaneous power) (7). However, too heavy a load will slow the jump down. The velocity of the jump has to be enough to allow maximal power output to be achieved.
Fortunately, measuring power output, or looking at changes in performance such as 20-metre sprint times, can identify the optimal load for squat jumps. One study looked at using either 30% or 80% loads of the subjects’ 1RM squat to perform squat jumps and then measure the changes in performance (8).
The 26 subjects followed an eight-week, twice-weekly training programme performing four sets of five jumps after warming up, with three minutes rest between sets. Both groups improved their 1RM and their peak power. The 30% group increased their peak velocity and decreased their 20m sprint times. The 80% group increased their 20m sprint times. So while both training modes were effective in increasing peak power and 1RM strength, the lighter loads had a much better impact on speed of movement.
This is obviously of importance to most coaches and athletes. However, it’s worth adding that the training history of this group of subjects was quite varied, and so this may be partly why they benefited from the lighter loads.
Another study looked at rugby league players who were strength and power trained and found that squat jumps with loads varying between 47 and 63% of 1RM were effective in improving power output(9). These players were strong athletes; the loads showing the highest power output were between 85 and 95kg, and one group of the players in the study had average 1RM for normal squats of 161kg.
The researchers found that using a load less than 47% 1RM did not result in enough resistance for peak power to be generated. But a load heavier than 63% 1RM resulted in too slow a movement. More generally, trained players may need higher loads to generate peak power because of their neural adaptations to strength and power training; they can simply recruit more of their muscle fibres to act in synchronisation quickly than non-trained individuals.
If you are intending to start using squat jumps, try sequencing them into your current strength-training programme. Having a minimum strength base of squatting 1RM equivalent to your own body weight is essential. A four-week, twice-weekly programme of four sets of five jumps at 30% of 1RM with three minutes rest between sets is a good start. As you become stronger you can alternate fortnightly between strength sessions and sessions incorporating squat jumps. When you can squat equivalent to twice your body weight for 1RM, then you can progress towards the jump squat load of 50%1RM.
References
1. JSCR 2005; 19(2):349-357
2. Bompa, T (1999) Periodization
3. JSCR 2005; 19(4):893-897
4. JSCR 2006; 20(1):162-166
5. JSCR 2002; 16(4):547-550
6. JSCR 2006; 20(2):268-272
7. J Sport Sci 2001; 19(2):99-105
8. JSCR 2002; 16(1):75-82
9. JSCR 2001; 15(1):92-97