Contemporary sprint training involves a variety of training units, typically with 2-3 maximal intensity sprint sessions per week, plus other recovery or conditioning work on alternate days. In general, programs of this nature are carried out for many weeks or months with the volume of work tapering off to a very low volume or even complete rest in the lead up to a major competition. Anecdotally, such programs make athletes run faster and their muscles contract more rapidly, however the critical components of such training i.e. low frequency of maximal intensity sprinting followed by tapering or detraining remain relatively unexplored in the scientific literature. Furthermore, many of the sprint studies that have examined muscle contractile adaptations have used muscle biopsies, an invasive procedure that often limits research participants to non-elite athletes and assesses only a small portion of a single muscle. Alternative non-invasive measures of muscle contractile parameters may provide useful information about adaptation to sprint training with elite sprint athletes. On the basis of their previously documented relationship to both muscle biopsy data and whole muscle force output, muscle twitch torque parameters (MTTPs) and muscle fibre conduction velocity (MFCV) were deemed as suitable non-invasive measures for investigation into muscle physiology/contractility in this thesis. The aims of this thesis were: (1) to compare sprint performance, MFCV and MTTPs between elite sprint and endurance trained athletes, and (2) to examine changes in sprint performance, MFCV and MTTPs in response to seven weeks of low volume and low frequency (≤3x per week) sprint training and seven weeks of detraining in previously untrained subjects.
The study described in Chapter 3 examines the reliability of those procedures used to measure MFCV and MTTPs. Fourteen moderately active subjects were each tested three times within a week, with vastus lateralis (VL) MFCV assessed via contractions elicited as a result of transcutaneous stimulation of the femoral nerve. Similarly, MTTPs were examined via direct trancutaneous stimulation of VL. Analysis showed MFCV had a mean coefficient of variation of 3.98%, while twitch parameters of peak torque (PT), rate of torque development (RTD), and rate of relaxation (RR) had mean coefficients of variation of 16.74, 18.79, and 18.62% respectively. Further analysis revealed that PT was highly correlated with RTD and RR (r=0.99 and 0.88 respectively) and that these latter measures could be semi-normalised by dividing by PT to give rate measures in units of percent PT per second; these measures resulted in substantially lower within-subject coefficients of variation for RTD and RR (5.8 and 10.53% respectively). It was concluded that MFCV measured in response to a contraction elicited via electrical nerve stimulation shows similar between-session repeatability to that reported in previous studies that have used voluntary contractions. Raw twitch torque parameters (PT, RTD, RR) however were less repeatable with the current methods but reliability of the rate measures were substantially improved when data were expressed as RTD/PT and RR/PT.
The purpose of the study described in Chapter 4 was to compare differences in MFCV, MTTPs, 40m sprint performance and isometric leg extension strength in ten (seven male, three female) elite sprint trained subjects and ten (seven male, three female) elite endurartce trained athletes using MTTPs and MFCV, and to examine the relationship of the tested variables with 40m sprint and voluntary isometric leg extension performance. Analysis showed that MTTPs RTD/PT and RR/PT were significantly greater amongst the sprint athletes and did correlate significantly with the strength (r=0.72, p<0.01 & r=0.43, p<0.05 respectively, n=20) and sprint performance variables (r=0.59, p<0.05 & r= 0.57, p<0.05 respectively, n=20). In contrast MFCV was not significantly different between groups and was not significantly related to the other dependant variables.
The final study (Chapter 5) examined changes in sprint and voluntary strength performance, MTTPs and MFCV adaptations to seven weeks of low volume sprint training (3x per week) and seven weeks of detraining. Of the 28 recreationally active subjects that completed the study, 15 comprised the training group (nine male, six female) and 13 (eight male and five females) acted as controls. Analysis showed significantly improved sprint performance as a result of training and that this was largely maintained throughout the detraining period; no significant changes were found in the control data. Pre-normalization muscle twitch torque parameters (e.g. PT) were significantly increased as a result of training and remained elevated during the detraining period (although the mechanisms for this are uncertain). In contrast, the control data showed no significant changes. With regard to the semi-normalised twitch torque measures amongst the training group, changes in both RTD/PT and RR/PT over the course of the 14 week study were significantly related to changes in sprint performance (r=-0.31-0.37 and 0.39-0.44 respectively). Despite these relationships no significant changes in RTD/PT and RR/PT were recorded during the training period. With detraining however, RTD/PT was significantly increased for the training group. RR/PT showed no significant changes throughout the course of the 14 week experimental period for either group. Muscle fibre conduction velocity did not significantly change in response to training or detraining.
In conclusion, this series of studies has demonstrated measurable differences in muscle contractile parameters through non-invasive means which discriminate between sprint and endurance trained athletes in the same manner as a muscle biopsy would be expected to. Similarly as would be expected with biopsy data, changes in MTTP as a result of training and detraining are related to changes in sprint performance. Furthermore, changes in the MTTPs data in response to detraining tend to suggest a shift towards more rapid torque development, a result that is consistent with previous twitch torque and muscle biopsy data in resistance training studies. Finally, in contrast to previous literature MFCV did not appear to discriminate between sprint and endurance trained athletes.