Reliability of isokinetic bench press

Table 2. Reliability indices ICC[2,11, SEM, SDD, and CV

careful in extrapolating these values to other populations like patients or men or to other exercises. Furthermore, the CV gives an idea of the absolute reliability, and this reliability index shows that lowvelocity bench press measurements had higher reliability than moderate-velocity bench press measurements, apparently because higher measurement errors appear at lower absolute values (Holmback et al., 1999). Interpretation of the results should therefore be based on both absolute (ICC) and relative (SEM, SDD, and CV) indices.

Many researchers have described the advantages of isokinetic training and testing in general, including safety, the possibility of accommodating (optimal) resistance through the total ROM, and the facility for muscle force analysis (Abernethy et al., 1995; Osternig, 1986). The system reliability of computerized isokinetic strength testing equipment has been reported to be relatively high (R2 > 0.95), but the intra-rater and inter-rater reliability is not always examined (Bandy & McLaughlin, 1993; Gleeson & Mercer, 1996). Few studies are found on inter-device reliability of isokinetic devices. Furthermore, a general disadvantage of isokinetic testing is its low task specificity, e.g., isokinetic movements do not occur in activities of daily living (ADL) or in sports (Morrissey, Harman, Johnson, 1995). It may be possible to describe some similarities between concentric isokinetic movements and swimming. Studies showed that, although the speed of the resistance arm is set to a specific velocity, acceleration and deceleration at the beginning and end, respectively, of the (ROM) are present and therefore the researcher should be able to control the linearity of the movement of the resistance arm through the whole ROM (Gransberg & Knutson, 1983). Note that an isokinetic movement does not mean muscle shortening at constant velocity (Osternig, 1986), especially when twojoint motions are involved.

The Arial computerized exercise system (ACES) has some general advantages and disadvantages. The ACES isokinetic mode makes it possible to study relationships between slow and (very) fast velocities and muscular performance in functional movements like benchpress, squats, pull-downs, shoulder press, etc. According to the manufacturer it is possible to perform over 20 different exercises on the ACES. The commercially available software program of the device

calculates the mean of the three repetitions and provides a Root Mean Square (RMS) of each set. The protocol used made it not easy to study the nine repetitions separately, and the researcher had little or no influence on the values. Each contraction is influenced by a large number of factors, e.g., stabilization during the experiment (Smith, 1994), delayed muscle soreness (Friden & Lieber, 1992), learning processes (Gleeson & Mercer, 1996), time of day (Gleeson & Mercer, 1996), and feedback (Hobbel & Rose, 1993). These factors make each repetition, each set, and each occasion unique. There is a possibility that the relative short resting time between the three repetitions affects the results. To check the intraset variability we divided the RMS-value with its mean, and this showed that in 97.8% of the total amount of sets the RMS was lower than 10% of the mean, indicating low intraset variability.

Compared with the studies of Hortobagyi and Katch (1990) and Jacobs and Pope (1986), the subjects in this study were lying in the opposite direction to stabilize the lower back. It is of great importance to stabilize the trunk to be able to perform at maximum with the arms. Another difference between these earlier reliability studies and our study is that in our study other statistical methods (recommended by Holmback et al., 1999) and healthy women were used. Jacobs and Pope (1986) attempted to obtain normative data and included 11 women (military recruits) in their study. Questions can be raised as to how useful these normative values are when only 11 subjects were included. In particular, the inter-device reliability of ACES should be tested to be able to generalize these results and our results.

One could question the clinical value of measuring `peak value' in an open-chain movement. For example, when a patient is not able to perform an ADL movement, it is not the maximal strength but the minimal strength somewhere in the ROM that sets the limit. Increasing the maximal strength may not help the patient in performing the movement, but finding the weakest point and training on that particular movement or training throughout the whole ROM will logically increase functional capacity. Strength testing should therefore concentrate more on power and/or work measurements in order to understand human performance in complex functional movements. The performance parameter `total work' showed the highest values at SDD indicating low sensibility. This means

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