En reinvención constante

Izquierdo et al (1999) investigated the strength and power characteristics in middle aged (n = 26, mean age 46 years) and elderly men (n = 21; mean age 65 years), assessing power across a spectrum of loads (0, 15, 30, 45, 60, 70% 1-RM) during the Smith-machine half squat, revealing that peak power occurred between 60-70% 1-RM, with no differences between groups. A subsequent study by the same group of researchers found that 1-RM Smith-machine half squat significantly increased along with peak power output during the half squats across a spectrum of loads (15, 30, 45, 60, 70% 1-RM) after 16 weeks of strength training in middle aged (46 ± 2 yr) and older (64 ± 2 yr) men (Izquierdo et al., 2001b). Both pre and post training the participants’ peak power occurred between 60-70% 1-RM, as reported in their previous study (Izquierdo et al., 1999). A further study using the same methods in middle aged (n = 26, mean age 46 yr) and elderly men (n = 21, mean age 64 ± 2 yr) also reported peak power occurred between 60-70% 1-RM, although the younger and stronger group developed peak power at 60% 1-RM where as the older and weaker group developed peak power at 70% 1-RM, highlighting a decline in force and power production with increasing age (Izquierdo et al., 2001a). It is worth noting however, that power in the aforementioned studies was calculated using inverse dynamics and excluded body mass in the calculation resulting in very low power values, (the implications of such methods of assessing power are discussed in detail in Chapter 3.1).

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Siegel et al. (2002) used college age resistance trained subjects (n=25) to investigate the load which elicits peak power during squats performed on a Smith machine, with power calculated using inverse dynamics and related this to muscle fibre distribution from muscle biopsies of the vastus lateralis. Results revealed that peak power occurred between 50-70% 1-RM, similar to the findings in older subjects (Izquierdo et al., 1999; Izquierdo et al., 2001a; Izquierdo et al., 2001b), but no relationships between performance measures and muscle fibre distribution were observed. Similar findings were observed in well trained male sprinters (n=10), with half squats performed on a Smith machine. Power was calculated from the product of vertical ground reaction force (assessed using a force plate) and bar velocity (assessed using a LPT), revealing that peak power occurred at 60% 1- RM (3134.3 ± 561.9 W) although this was not significantly different (p>0.05) when compared to peak power at any other load (30, 45, 60, 70, 80% 1-RM). While the Smith machine improves the accuracy of the assessment of velocity by preventing any horizontal displacement of the bar, it limits the application of these findings to free weight back squats, which are more commonly performed during strength training programmes. It is also worth noting that using combined kinetic (force collected via the force platform) and kinematic (velocity calculated via bar displacement time data) methods to calculate power are limited, as Lake et al. (2012) revealed that velocity of the bar does not reflect velocity of the COM of the body or system.

Zink et al. (2006) investigated the effects of load (20-90% 1-RM in 10% increments) on peak power, force and barbell velocity during free weight back squats, in 12 experienced lifters. The authors observed no significant difference (p>0.05) in peak power output across loads, although the highest values occurred at 40-50% 1-RM. There was, however, a progressive increase in peak ground reaction force and a progressive decrease in bar velocity with an increase in load. The slightly lower PMax loads in this study compared to the aforementioned studies may be explained

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by the fact that this was the only study to assess free weight back squat performance, along with the use of older, less well trained participants in the previous studies (Izquierdo et al., 1999; Izquierdo et al., 2001a; Izquierdo et al., 2001b).

Cormie et al. (2007c) compared six different methods of assessing power during squats, squat jumps and power cleans across a spectrum of loads: one linear position transducer (LPT) (including barbell mass), one LTP (including system mass), two LPT’s, FP only, FP plus one LPT and a FP plus two LPT’s, in well trained males. Results demonstrated that one LPT plus barbell mass under- valued force and therefore power during the squat and jump squat, where as the one LPT and two LPT methods (including system mass) over-valued force and therefore power in line with the findings of Hori et al. (2007) during the hang power clean and squat jump. During the squat, the use of 1 LPT and 2 LPT’s resulted in the identification of an optimal load of 30% 1-RM (4215.07 ± 1227.11 W; 4104.24 ± 1162.01 W, respectively), whereas the methods using kinetic data (FP, FP plus 1 LPT) identified optimal load as 71% 1-RM (3243.66 ± 448.78 W, 3291.28 ± 326.41 W, respectively) and (FP plus 2 LPT) 56% (3206.32 ± 411.49 W), although peak power values differed across all methods. The authors conclude that methods of assessing power need to be standardised to ensure that findings between studies are comparable. These findings and recommendations for the back squat have been supported by a series of other studies published by these authors (Cormie et al., 2007a; Cormie et al., 2007b; Cormie et al., 2007e; McBride et al., 2011).

These results appear to demonstrate that peak power output during squats occur across a spectrum of loads, which is influenced by the methods used to assess power (kinetic, kinematic or combined methods), the mode of activity (free weight versus Smith machine) and possibly training status. If assessed during free weight back squats in trained individuals peak power appears to occur between

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40-50% 1-RM if assessed based on bar velocity (inverse dynamics) (Zink et al., 2006), or ~70% if assessed from force time data (forward dynamics) (Cormie et al., 2007c; Cormie et al., 2007b).