Week 14 - Strength Training BW PDF

Strength training Learning outcomes u Understand the ways in which resistance training induces task-specific, but not muscle-specific, effects u Understand that resistance training can provide benefits for older adults that it does not provide for younger adults u Expl...

Strength training Learning outcomes u Understand the ways in which resistance training induces task-specific, but not muscle-specific, effects u Understand that resistance training can provide benefits for older adults that it does not provide for younger adults u Explore the effects of resistance training on the central nervous system Specificity of resistance training effects Training effects are also specific to the trained task u One-legged isometric extension training reduces fatigability on one-legged task but not two-legged task u Two-legged training reduces fatigability on two-legged but not one-legged task Rube and Secher (1990) u Training: 150 task repetitions u Fatigue: Decline in max force over 150 task repetitions Training effects are less specific to trained muscles u 4 weeks of strength training increased hand muscle strength by ~30% u Toe extensor muscles did not change in strength BUT... u Muscle strength increased by ~14% in the untrained hand Yue and Cole (1992) But actual training may not be critical... u 4 weeks of strength training increased hand muscle strength by ~30% u 4 weeks of imagined strength training increased hand muscle strength by ~22% u 4 weeks of no real or imagined strength training did not change hand muscle strength Yue and Cole (1992) u Hand muscles are trainable in this way but not elbow flexors or knee extensors u Due to differences in maximality??? Training effects are also specific to the velocity of training movements u People performed isokinetic or isometric resistance training at 5.23 m/s for 16 weeks u Increase in maximum voluntary torque was greatest at the training speed u Isometric training with a metronome also produced the greatest MVT at 5.23 m/s u Effects of strength training are greatest for movements made at the training velocity Behm and Sale (1993) u Implications for different athletes? Isometric Isokinetic Motor asymmetries can be trained away u Bilateral deficit: The MVC in a muscle is reduced if the homologous muscle in the opposite limb is contracted. u Right MVC + Left MVC > Right + Left MVC u Bilateral deficit during slow contractions is ~20% u During rapid contractions this can be as high as ~45% Koh et al. (1993) u Why might this occur? Bilateral deficit can be trained away u Athletes such as rowers or weightlifters who train both sides of their body simultaneously can eliminate bilateral deficit u They eventually obtain bilateral facilitation where they produce the greatest amount of force only when contracting homologous muscles on both sides of their body Howard and Enoka (1991) u How could this concept be beneficial following stroke? Muscle coactivation can be trained away u Cocontraction of muscle producing opposing torques about a joint is inefficient for movement production BUT u Cocontraction seems to be a default strategy of the motor system to cope with situations where there is uncertainty Muscle co-activation can be trained away u An 8-week resistance training program increased the strength of knee extensors and reduced the amount of coactivation with knee flexors Carolan and Cafarelli (1992) u Most of the decrease in co-contraction occurred within the first week of training u Resistance training can produce improved coordination before large changes in strength Is strength training more than it appears? u Learning a novel task is also capable of reducing unnecessary/inefficient co-contraction of muscles Person (1958) u Can we say that the initial phase of strength training involves a period of motor learning followed by relatively rapid increases in strength? u What does that imply about the type of resistance training exercises we should prescribe for specific activities? Resistance training for older adults Resistance training increases motor unit firing rates in elderly u Increases in MVC after an 8-week resistance training program associated with increased motor unit firing rates in elderly but not young people Kamen and Knight (2004) A question just for you u Which motor system structures are responsible for increasing force output following a program of resistance training? Read the introduction (at least) of the article posted on Moodle – this question will appear in the final quiz!