Showing papers by "Alun G. Williams published in 2010"

Inter-individual variability in the adaptation of human muscle specific tension to progressive resistance training

Abstract: Considerable variation exists between people in the muscle response to resistance training, but there are numerous ways muscle might adapt to overload that might explain this variable response Therefore, the aim of this study was to quantify the range of responses concerning the training-induced change in maximum voluntary contraction (MVC) knee joint torque, quadriceps femoris (QF) maximum muscle force (F), physiological cross-sectional area (PCSA) and specific tension (F/PCSA) It was hypothesized that the variable change in QF specific tension between individuals would be less than that of MVC Fifty-three untrained young men performed progressive leg-extension training three times a week for 9 weeks F was determined from MVC torque, voluntary muscle activation level, antagonist muscle co-activation and patellar tendon moment arm QF specific tension was established by dividing F by QF PCSA, which was calculated from the ratio of QF muscle volume to muscle fascicle length MVC torque increased by 26 ± 11% (P < 00001; range −1 to 52%), while F increased by 22 ± 11% (P < 00001; range −1 to 44%) PCSA increased by 6 ± 4% (P < 0001; range −3 to 18%) and specific tension increased by 17 ± 11% (P < 00001; range −5 to 39%) In conclusion, training-induced changes in F and PCSA varied substantially between individuals, giving rise to greater inter-individual variability in the specific tension response compared to that of MVC Furthermore, it appears that the change in specific tension is responsible for the variable change in MVC

Resistance training increases in vivo quadriceps femoris muscle specific tension in young men.

Abstract: Aim: The present study investigated whether in vivo human quadriceps femoris (QF) muscle specific tension changed following strength training by systematically determining QF maximal force and physiological cross-sectional area (PCSA). Methods: Seventeen untrained men (20 +/- 2 yrs) performed high-intensity leg-extension training 3 times a week for 9 weeks. Maximum tendon force (F(t)) was calculated from maximum voluntary contraction (MVC) torque, corrected for agonist and antagonist muscle activation, and moment arm length (d(PT)) before and after training. QF PCSA was calculated as the sum of the four component muscle volumes, each divided by its fascicle length. Dividing F(t) by the sum of the component muscle PCSAs, each multiplied by the cosine of the respective fascicle pennation angle, provided QF specific tension. Results: MVC torque and QF activation increased by 31% (P < 0.01) and 3% (P < 0.05), respectively, but there was no change in antagonist co-activation or d(PT). Subsequently, F(t) increased by 27% (P < 0.01). QF volume increased by 6% but fascicle length did not change in any of the component muscles, leading to a 6% increase in QF PCSA (P < 0.05). Fascicle pennation angle increased by 5% (P < 0.01) but only in the vastus lateralis muscle. Consequently, QF specific tension increased by 20% (P < 0.01). Conclusion: An increase in human muscle specific tension appears to be a real consequence of resistance training rather than being an artefact of measuring errors but the underlying cause of this phenomenon remains to be determined.

Inter-individual variability in adaptation of the leg muscles following a standardised endurance training programme in young women.

Abstract: There is considerable inter-individual variability in adaptations to endurance training. We hypothesised that those individuals with a low local leg-muscle peak aerobic capacity \( (\dot{V} {\text{O}}_{{2{\text{peak}}}}) \) relative to their whole-body maximal aerobic capacity \( ( \dot{V} {\text{O}}_{2\max}) \) would experience greater muscle training adaptations compared to those with a relatively high \( \dot{V} {\text{O}}_{{2{\text{peak}}}} \). 53 untrained young women completed one-leg cycling to measure \( \dot{V} {\text{O}}_{{2{\text{peak}}}} \) and two-leg cycling to measure \( \dot{V} {\text{O}}_{2\max} \). The one-leg \( \dot{V} {\text{O}}_{{2{\text{peak}}}} \) was expressed as a ratio of the two-leg \( \dot{V} {\text{O}}_{2\max} \) (Ratio1:2). Magnetic resonance imaging was used to indicate quadriceps muscle volume. Measurements were taken before and after completion of 6 weeks of supervised endurance training. There was large inter-individual variability in the pre-training Ratio1:2 and large variability in the magnitude of training adaptations. The pre-training Ratio1:2 was not related to training-induced changes in \( \dot{V} {\text{O}}_{2\max} \) (P = 0.441) but was inversely correlated with changes in one-leg \( \dot{V} {\text{O}}_{{2{\text{peak}}}} \) and muscle volume (P < 0.05). No relationship was found between the training-induced changes in two-leg \( \dot{V} {\text{O}}_{2\max} \) and one-leg \( \dot{V} {\text{O}}_{{2{\text{peak}}}} \) (r = 0.21; P = 0.129). It is concluded that the local leg-muscle aerobic capacity and Ratio1:2 vary from person to person and this influences the extent of muscle adaptations following standardised endurance training. These results help to explain why muscle adaptations vary between people and suggest that setting the training stimulus at a fixed percentage of \( \dot{V} {\text{O}}_{2\max} \) might not be a good way to standardise the training stimulus to the leg muscles of different people.

Can forefoot varus wedges enhance anaerobic cycling performance in untrained males with forefoot varus

Abstract: There is limited research relating to cycling biomechanics, and more specifically, the use of foot orthotics to enhance cycling performance. Therefore, this study investigated the effect of forefoot varus wedges (foot orthotics) on cycling performance, as measured by anaerobic power output in a population of untrained males presenting with forefoot varus. Six untrained males (forefoot varus mean ± SD; 6.1 ± 1.7°) completed two separate 30 s Wingate Anaerobic tests (WAnT) on a Monark 824E cycle ergometer, one with and one without varus wedges, in a counterbalanced order. Although paired-sample t-tests revealed no significant difference P > .05 in mean power, peak power, and anaerobic fatigue between the two conditions, a Pearson’s productmoment correlation coefficient (r = .957, n = 6, P = .003) demonstrated that varus wedges offer greater performance benefits to riders with greater forefoot varus. These preliminary data suggest that correcting forefoot varus using wedges may improve shortterm power output during cycling for individuals possessing high levels of forefoot varus.