The effects of strength training on isometric force production symmetry in recreationally trained males

Abstract

Objectives:The purpose of this investigation was to determine what effect a bilateral strength training regimen has on isometric force production symmetry and if changes in force production symmetry can be accounted for by differences in pre-intervention strength levels. Design: Sixteen recreationally trained males (1-RM squat: 146.8 ± 23.0 kg.) were assigned to two groups for the 7-week training intervention: strong (S) and weak (W) based on pre-training squat isometric peak force allometrically scaled (IPFa) at 120° knee angle. Methods: Subjects completed a 7-week training intervention following a block-periodized model and were tested on measures of dynamic (1RM squat) and isometric (isometric squat at 90° and 120° knee angle) strength pre-and post-intervention. The degree of bilateral lower limb asymmetry was calculated as a percentage where 0% symmetry index (SI) indicates perfect symmetry on the isometric squat. Results: ANCOVA results showed no statistical difference between groups for all dependent variables when pre-intervention IPFa 120° scores were used as the covariate. Paired t-tests results showed both groups statistically improved 1RM squat and IPFa 120° (p < 0.05). IPFa 120° SI decreased statistically from pre-training in the W group (p = 0.03). Independent t-test results showed the W group had statistically larger pre-intervention SI scores for IPFa 90° (p = 0.045) and IPFa 120° (p = 0.007); however this difference was no longer present following strength training. There was a strong inverse relationship between pooled IPFa 120° and IPFa 120° SI (r = -0.64, p = 0.004). Conclusions:The findings of the current study support the notion that weaker individuals can augment lower limb symmetry with strength training. The same does not seem to be true for stronger individuals who already have a low symmetry index score. These findings indicate that strength training improves force production symmetry in relatively weak males, which may be important for bilateral tasks and injury potential reduction.(Journal of Trainology 2014;3:6-10)

Do stiffness and asymmetries predict change of direction performance?

“…Between-group analyses also indicated a 'large' and significant difference between median-split fast and slow performers. Whilst previous investigations have associated asymmetries in force-related parameters with impaired athletic performance (Bailey et al, 2013;Bailey et al, 2015;Bazyler et al, 2014;Bell et al, 2014;Hart, Nimphius, et al, 2014), the relationship between asymmetry and CODS is not clear. Two investigations have noted reductions in CODS performance where an eccentric strength asymmetry is apparent (Chaouachi et al, 2012;Lockie et al, 2012).…”

“…It is therefore conceivable that the observed association between asymmetry and CODS performance is purely indicative of participants' current athletic ability or training status. Indeed, Bazyler et al (2014) reported that asymmetries are likely to be greater in weaker individuals. Across a seven week bilateral training programme, Bazyler et al (2014) also noted that as strength increased there was a concomitant decrease in asymmetry in weaker individuals.…”

“…Indeed, Bazyler et al (2014) reported that asymmetries are likely to be greater in weaker individuals. Across a seven week bilateral training programme, Bazyler et al (2014) also noted that as strength increased there was a concomitant decrease in asymmetry in weaker individuals. Future investigations should seek to determine whether asymmetries in the variables highlighted in the current study are associated with CODS in an athletic population.…”

“…It has since been observed that the expression of vertical stiffness and associated asymmetries is highly task dependant (Maloney, Fletcher, & Richards, 2015). As a change of direction may be characterised as acyclic, ballistic and unilateral in nature, the unilateral drop jump is likely to demonstrate the greatest correspondence to CODS and may therefore carry greater validity as an assessment for vertical stiffness Several investigations have reported that asymmetries in force/power qualities may be detrimental to athletic performance (Bailey, Sato, Alexander, Chiang, & Stone, 2013;Bailey, Sato, Burnett, & Stone, 2015;Bazyler, Bailey, Chiang, Sato, & Stone, 2014;Bell, Sanfilippo, Binkley, & Heiderscheit, 2014;Hart, Nimphius, Spiteri, & Newton, 2014), however, this relationship is not clear in regards to CODS. Whilst eccentric strength asymmetry has been linked to impaired CODS in some investigations (Chaouachi et al, 2012;Lockie, Shultz, Jeffriess, & Callaghan, 2012), Lockie et al (2014) reported that athletes with 'typical' asymmetries in unilateral jump performance (vertical jump: ∼10%; horizontal jump: ∼3%; lateral jump: ∼5%) did not experience speed detriments.…”

Training Methods and Considerations for Practitioners to Reduce Interlimb Asymmetries

“…With that in mind, a number of studies have reported how inter-limb asymmetries have changed following a targeted training intervention (4,8,11,12,19,30). This article will provide an overview of the available literature and suggest evidence-based methods to reduce interlimb differences.…”