Strength training: resistance exercises to improve strength and power

Contrast training enhances power workout quality – but only if you’re already quite strong.

Controlled scientific research suggests these benefits are real, if a bit over-inflated. In one study, athletes performing explosive jump-squats, after a set of relatively heavy-resistance half-squats, were able to jump a statistically significant 2.8% higher than they were without the half-squats. The researchers suggested that this difference occurred because the heavy squats produced a ‘potentiation’ effect which allowed muscles to contract more quickly and forcefully. This response was believed to be particularly noticeable in fast-twitch motor units – collections of muscle cells with an intrinsic ability to shorten at high speeds.

Supporting work carried out by the noted German scientist Dietmar Schmidtbleicher found that three maximal voluntary contractions of the quadriceps muscles led to a 3.3% rise in counter-movement jumpheight for both male and female athletes, (counter-movement jumps involve springing upwards as high as possible from a crouching position). In Schmidtbleicher’s investigation, the height of drop-jumps (performed by jumping down from a platform then springing up explosively) also improved after maximal quadriceps, and explosive force and movement velocity were greater during bench throws after upper-body maximal voluntary contractions.

Note that this positive effect of prior heavy exertion on subsequent power is somewhat counter-intuitive. One might expect that maximal or near-maximal contractions against heavy resistance would induce some level of fatigue that would subsequently retard explosive movements, but instead well-controlled high-load work often seems to facilitate subsequent powerful actions.

Although there has been general agreement that combining high-resistance work with lighter, quicker movements during training produces optimal gains in power, there has been some debate about exactly how the two types of strength training should be combined within workouts. There are basically two schools of thought: proponents of ‘complex training’ believe that various sets of groups (complexes) of exercises should be performed in such a way that several sets of heavy-resistance exercise are followed by several sets of lighter-resistance; proponents of ‘contrast training’, on the other hand, suggest that heavy and light exercises should be alternated, set for set, with a lightning-fast, light-resistance set always following a heavy one.

Intriguing Aussie half-squat study tests the different workouts

To see which form of training produced higher-quality workouts, Australian scientists recently carried out an intriguing study of three different types of weight training with 11 female national or international hockey and softball players, aged 19-31. The athletes normally strength-trained for about five hours each week on top of 15 hours of sport-specific training, and all had been strength-training regularly for more than two years. They were thus well used to performing the half-squats and jump squats, which were used for the study.

The half-squats were performed on a Smith machine, with the down-position (squat-position) knee angle set at 90° and the intensity fixed at 3RM (i.e. the three-repetition maximum, the maximal amount of weight which could be squatted successfully three – and only three – times). This 3RM resistance averaged 120.5kg for the 11 athletes.

By contrast, the jump squats were completed with a modified Smith machine positioned over a force plate. This machine was three metres high to permit safe completion of the jumps. Its bar was fixed so that it could move only vertically, and a (light) resistance of just 30% of the 1RM half-squat (or about 32% of the 3RM half-squat resistance) was used as the load, primarily because it had been previously found to produce maximal mechanical power outputs; this load averaged 38kg. The athletes had to keep the bar in contact with their shoulders at all times, and any failure to do so was considered a false trial. Once again, a knee angle of 90° was selected for the squat position. The explosive jump for height was undertaken from this position; thus, the jump itself involved a purely concentric action of the quads, which helped to control the influence of muscle pre-stretch on performance. Four reps of jump-squats were performed per set. Naturally, the half-squats at 3RM were considered to be the heavy-load exercise, while the jump squats at 32% of 3RM represented the explosive exertion.

As mentioned, three different workouts were conducted. In a ‘traditional’ workout, the 11 athletes completed three sets of light-load exercise (the jump squats), then three sets of heavy-load work (half-squats); this is considered traditional because athletes often move from lighter to heavier loads over the course of a workout. In a second ‘complex’ workout, all sets of the heavy-load half-squats were performed before the three sets of explosive jump squats. Finally, in the ‘contrast’ session, a set of the heavy half-squats was alternated with a set of the lighter jump-squats until three sets of each exercise had been performed. Each type of workout was preceded by identical thorough warm-ups, including stationary cycling, light static stretching and submaximal half-squats.

Complex workout produces fatigue

Interestingly enough, the difference in power performance during the different squat-training methods in the Australian study depended on the athletes’ strength levels, so the 11 subjects were ‘median-split’ (with the median athlete ‘thrown out’) into two groups, with the five athletes with the highest 1RM values in one group and the five with the lowest in the other. 1RM averaged 116kg for the low-strength groups and 139kg for the high-strength athletes. After this split, statistical analysis revealed that the higher-strength group achieved a greater improvement in jump-squat performance with the contrast workout than with the traditional method, but no such difference was observed in the lower-strength athletes.

Contrast method works best for those who are already strong

Basically, the higher-strength group achieved a 2% higher increase in maximal force and a 4% greater rise in peak power during squat jumping with the contrast training method than with the traditional method, even though in the latter workout all of the squat jumping was performed before any potentially fatiguing heavy-load training could occur. Notably, however, the lower-strength group tended to fare worse with the contrast workout, producing about 1% less maximal force and peak power than they had with the traditional session. The Australian researchers concluded that contrast training is advantageous for increasing power output in athletes with relatively high strength levels.

This is a reasonable conclusion. In a separate study, stronger subjects had greater gains in jump-squat performance after completing one set of heavy (5RM) squats than weaker individuals, and in another very interesting investigation, highly trained athletes displayed a significant neuromuscular potentiation response after heavy-load exertion, whereas less well-trained physical education students did not (4). It is not clear whether the higher response observed in better-trained athletes is a consequence of their heightened fatigue resistance during initial heavy-load exercise or their more responsive neuromuscular systems, which become more ‘fired up’ by the vital, high-intensity work (i.e. their potentiation effect is greater).

Overall, there was a trend for performance during the jump squats to decrease over the course of each type of workout; however, the contrast technique tended to produce the smallest decrement in performance, possibly because the potentiation effect mentioned above counterbalanced increased fatigue over the course of the workout. Because contrast training worked well with the strong athletes but not the weaker ones, the Australian researchers suggest that athletes should develop a very advanced strength base before considering this method of power development.

If such a base were indeed developed, what might a contrast workout actually look like for an athlete attempting to develop power? For an athlete who runs in his/her sport and wants to improve raw running speed, explosive sprints, jumps, hops, bounds and high-intensity drills might be alternated with heavy-load exercises such as half-squats, partial squats, bench step-ups and so on, using a barbell to provide resistance. For a cyclist, the explosive sprints and movements could be alternated with high-load leg presses and bicycle leg-swings carried out with elastic stretch cords with very high resistance.

Interestingly enough, it is not known how long the potentiation effect actually lasts. For example, if an athlete completed a set of 4RM squats, would the resulting potentiation last for only one subsequent set of explosive activities, or might it linger for several sets of different explosive routines? An understanding of the ‘window of potentiation’ is lacking, and indeed this window might vary significantly from athlete to athlete. The research in this area is incomplete, but it is clear that it might be advantageous – as long as the potentiation window is fairly broad – to limit the total number of heavy-load moves within an overall contrast workout (to obviate the risk that fatigue resulting from heavy-load work would reduce the quality of the highly desired explosive movements). For now, athletes will have to experiment with their workouts to determine which combination of heavy- and light-load exercise seems to work best.

It is also very interesting to note that submaximal contractions of less than 85% of 1RM probably do not induce potentiation of the neuromuscular system. Thus, if one is attempting to construct a contrast workout in order to enhance power development, it is very important that quite high resistances be used for the slower, heavy-load interludes. Squatting at just 80% of max, for example, might only serve to boost fatigue without potentiating anything. It is also believed that the heavy contractions must be sustained for several seconds at a time for potentiation to occur.

Implications for warm-up routines, too

Note that the contrast technique results have profound implications, not just for workouts but also for warm-ups. If the competitive effort involves explosive movement, it is clear that the inclusion of heavy-load exercise within the warm-up will be far more beneficial to a strong, experienced athlete than a traditional warm-up of lower intensity, which attempts only to activate the cardiovascular system and ‘warm up’ the muscles in a more moderate way. Indeed, several studies have already shown that warming up with a heavy load produces enhanced ‘acute’ efforts (short-duration efforts which involve a quick burst of activity). For example, the use of a preparatory heavy load augments explosive countermovement jump height, drop-jump height, standing-long-jump-performance, general jumping ability and throwing speed.

So what’s the bottom line? ‘Complex’ workouts, in which all the heavy-load sets precede the initiation of light, explosive work, appear to produce enough fatigue at the onset of the explosive training to reduce the quality of work carried out. Athletes who have developed a good foundation of strength seem to be able to carry out higher-quality explosive work with contrast training techniques than with traditional schemes, in which light, fast work precedes the heavy-load training.

Owen Anderson