Cross-sectional and longitudinal uses of isoinertial, isometric, and isokinetic dynamomety

The purposes of this investigation were to assess whether maximal isoinertial (triceps pushdown [TP] and triceps extension [TE]), isometric and isokinetic (1.04, 2.08, 3.14, 4.16, and 5.20 rad·s -1 ) forearm extension strength measures: 1) presented statistical generality when they were correlated prior to and following 4, 8, and 12 wk of resistance training; 2) were similarly affected by training; and 3) presented statistical generality when their changes as a consequence of training were intercorrelated. Fifteen men (11 experimental and 4 controls) without a history of resistance training participated in the study. Training involved four sets of 8-12 repetitions, each followed by 90-s recovery, at 70-75% one repetition maximum (1RM), three times a week, for 12 wk. Training incorporated the TP, close-grip bench press, and triceps kickback exercises. Prior to and after 4, 8, and 12 wk of training, the intercorrelations among the TP, isometric, and isokinetic indices almost always achieved statistical generality (i.e., r 2 > 0.5). It was concluded that the strength measures generally discriminated similarly between subjects. However, the sensitivity of the strength measures to the effects of training were dissimilar. While all strength indices increased with the training, the timing(isoinertial prior to isometric and isokinetic adaptations) and magnitude(TP>TE> isometric>isokinetic) of these adaptations varied greatly. None of the intercorrelations between changes in the strength indices achieved statistical generality. Furthermore, factor (F)-analyses on these changes indicated that in the initial and later stages of training, there were three and four discrete factors, respectively, accounting for strength development. These factors were thought to reflect differential effects of training on the structural, neural (including learning), and mechanical mechanisms underpinning each strength index. Possible applications of this research design in better understanding strength development were also canvassed. bench press and a maximal isometric chest task (r = 0.6). Additional research is required to determine why there are these inconsistencies within the literature. A fundamental intrasubject issue is whether the effects of training interventions are detected by various forms of dynamometry. This issue can be addressed at several levels. The first level disregards sensitivity, and asks whether all forms of dynamometry detect changes in strength arising from an intervention. Again the data are equivocal. Twelve weeks of squat and bench press training at 6-RM loads has been shown to significantly increase 1RM squat and isometric leg strength values (3). While in contrast, 8-wk isokinetic training of one leg produced significant increments in isokinetic, but not 1RM, strength; and isoinertial training of the contralateral limb increased 1RM, but not isokinetic strength (18). More research is required to delimit when various forms of dynamometry are sensitive to the effects of particular regimens for given individuals. Second, even if various strength indices detect the effects of intervention, can it be assumed that they are similarly sensitive? The fact that several authors have reported that resistance training increases strength in one modality, but not another, indicates that sensitivity varies between strength measures (7,22). Third, are the various forms of dynamometry that are sensitive to interventions being modified by similar mechanisms? The poor intercorrelation between changes in isometric chest and 1RM bench press strength (r = 0.1) reported by Baker et al.(3) suggested not. Clearly, it is essential to determine the number, sequence, and nature of mechanistic events underpinning changes in particular strength indices if we are to: 1) make inferences from these strength indices to other structural contexts; and 2) better understand the effects of particular