Comparison of stable load, unstable load and variable resistance training interventions

Two alternate loading strategies that are increasingly prevalent within athletic, rehabilitation and general settings are unstable load and variable resistance training. However, the relative effectiveness of these strategies compared with conventional stable load training is unclear. We compared three different 4-week resistance training interventions using unstable loads, variable resistance, or traditional stable loads (i.e., barbells, dumbbells), on measures of strength, power, endurance and stability, as well as acceleration and change of direction performance. Twenty-seven recreationally trained males (age 23.4 ± 2.9 years; resistance training experience 4.1 ± 2.8 years, mean ± SD) participated in this study. A single leg quiet stand; single leg land-and-hold; countermovement jump; 10-metre sprint; modified 5-0-5 change of direction test; the athletic shoulder test; isometric mid-thigh pull; 30° isometric hamstring test; and the 60° trunk flexion test were measured before and after each of the three interventions. There were significant improvements in shoulder strength for all three groups, and improvements in other measures: isometric hamstring strength (stable, variable training) stability (stable and unstable), core endurance (unstable, variable), 10 m sprint (unstable) but not in countermovement jumping, or change of direction running. It appears that training with an unstable load can yield substantial improvements in core endurance, whereas the use of variable resistance loads showed improvements in isometric shoulder strength across a range of positions. All three forms of resistance training loads (stable, unstable, variable) offer athletes and coaches the opportunity to target discrete strength, power, endurance and stability qualities.