Allan J Davie

A Comparison of Strength and Power Characteristics Between Power Lifters, Olympic Lifters, and Sprinters

The purpose of this investigation was to determine the effect of involvement in power lifting, Olympic lifting, and sprinting on strength and power characteristics in the squat movement. A standard one repetition maximum squat test, jump squat tests, and vertical jumps with various loads were performed. The power lifters (PL, n = 8), Olympic lifters (OL, n = 6), and sprinters (S, n = 6) were significantly stronger than the controls (C, n = 8) (p <= 0.05). In addition, the OL group was significantly stronger than the S group. The OL group produced significantly higher peak forces, power outputs, velocities, and jump heights in comparison to the PL and C groups for jump trials at various loads. The S group produced higher peak velocities and jump heights in comparison to the PL and C groups for jump trials at various loads. The PL group was significantly higher in peak force and peak power for jump trials at various loads in comparison to the C group. The data indicates that strength and power characteristics are specific to each group and are most likely influenced by the various training protocols utilized.

Muscle activation of the knee extensors following high intensity endurance exercise in cyclists

Abstract This study was conducted to assess the effects in trained cyclists of exhausting endurance cycle exercise (CE) on maximal isometric force production, surface electromyogram (EMG) and activation deficit (AD) of the knee extensors. Ten male subjects made four isometric maximal voluntary contractions (MVC) of the knee extensor muscles immediately prior (pre), 10 min after (post) and 6 h after completion of CE. The CE consisted of 30 min of exercise on a stationary cycle ergometer at an intensity corresponding to 80% of maximal oxygen uptake (V˙O2max) followed by four × 60-s periods at 120% of V˙O2max. Two MVC were performed with recording of surface EMG from the knee extensors, whilst an additional two MVC were completed with percutaneous electrical muscle stimulation (EMS; 25 pulses at 100 Hz with the maximal tolerable current) superimposed over the maximal voluntary contraction force (MVF) but without EMG (to avoid interference). The MVF, integrated EMG (iEMG), and AD [calculated as the difference between MVF and the electrically stimulated force (ESF) during the EMS contractions] were statistically analysed. The MVF was significantly reduced (P < 0.05) post and 6-h post compared to pre-CE level. The iEMG was significantly reduced (P < 0.05) post and 6 h post CE. The ESF was also reduced, whilst AD was significantly increased (P < 0.05) post and 6-h post CE compared to the pre CE. These results suggest that the level of exercise stress administered in this study was sufficient to impair the central and peripheral mechanisms of force generation in knee extensors for a period of 6-h. Athletes engaged in concurrent training (strength and endurance) should consider this effect in exercise programming.

Neuromuscular responses to explosive and heavy resistance loading

The EMG power spectrum may shift towards higher frequencies with higher movement velocities. Fatigue, on the other hand, can cause a decrease in the frequency components. The purpose of this study was to examine acute effects of explosive (EE) and heavy resistance (HRE) concentric leg press exercise on muscle force, EMG and blood lactate. The EE included five sets of ten repetitions with 40+/-6% of the isometric maximum at a 100 degrees knee angle performed as explosively as possible. The same number of repetitions was performed in HRE but with a heavier load (67+/-7% of the isometric maximum at a 100 degrees knee angle). Maximal isometric and single concentric actions of different loads, and an isometric fatigue test were measured before and after both exercises. Surface EMG was recorded from the vastus medialis muscles for analyses of average EMG (aEMG) and EMG power spectrum. Muscle fiber composition of the vastus lateralis was determined and blood lactate measured throughout the exercises. Mean power frequency and median frequency were higher during EE than during HRE (P<0.05). They increased during EE (P<0.05) as the exercise progressed, whereas during HRE no change or even slight decreases were observed. Signs of fatigue after pure concentric work were not observed after EE, and even after HRE, possibly due to the relatively small range of motion and short duration of action time, the fatigue was not that extensive. The relative number of fast twitch fibers was correlated (r=0.87, P<0.05) with the change in blood lactate in HRE. It was concluded that there may be a greater use of fast twitch motor units in explosive movements and that instead of fatigue, the present number of concentric actions in explosive exercise seems to have facilitated the neuromuscular system.

Characteristics of titin in strength and power athletes

Abstract. The purpose of this investigation was to identify characteristics of the muscle protein titin in different athletic populations with increased levels of strength and power relative to non-athletes. Subjects fell into one of four groups: (1) non-athletes (NA) (n=5), (2) weightlifters (WL) (n=5), (3) powerlifters (PL) (n=5), (4) sprinters (S) (n=5). A one repetition maximum in the squat exercise was performed to assess strength. In addition, countermovement vertical jump trials were performed to assess power capabilities. Peak power (

The effect of endurance exercise on muscle force generating capacity of the lower limbs

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The acute effect of mouth only breathing on time to completion, heart rate, rate of perceived exertion, blood lactate, and ventilatory measures during a high-intensity shuttle run sequence.

) was calculated for the vertical jumps from force plate measurements. From gel electrophoresis analyses of muscle samples, titin-1 (T1) and titin-2 (T2) protein bands were identified, quantified and expressed relative to each other. In addition the relative mobility (Rf) of T1 and T2 was determined as an estimate of molecular weight. The NA group [%T1=47.8 (5.1), %T2=52.2 (5.1), mean (SE)] had lower T1 and higher T2 percentages than WL [%T1=62.3 (6.6), %T2=37.7 (6.6)], PL [%T1=66.8 (5.0), %T2=33.2 (5.0)] and S [%T1=65.9 (4.9), %T2=34.1 (4.9)] groups (P≤0.10, preliminary investigation into titin and exercise justifies more liberal alpha level). No significant differences were found in Rf of T1 or T2 between the groups. This investigation has shown that there is a differential expression of titin protein bands in competitive athletes with increased levels of strength and power in comparison to untrained non-athletic individuals. Some relationships between titin characteristics and athletic performance were observed; however, no conclusions can be made based on these data as to the contribution of titin to strength or power capabilities.

Significance of Prolonged Left Ventricular Wall Motion Abnormalities After Exercise Echocardiography Following Non–Q-Wave Acute Myocardial Infarction

Existing literature suggests that tests for maximal oxygen uptake (VO2max) should last 8-12 minutes and that prolonged tests do not produce valid measurements. The research underlying this suggestion has been performed with non-athletic populations and trained athletes may be more tolerant of longer protocols. Eleven rowers (8 males, 3 females) each underwent four different incremental tests on a standard rowing ergometer in randomised counterbalanced order. One of the tests was continuous with workload increments each minute (IT1MIN). This test lasted an average of 12 min+/-4 s (SEM). The other three tests were discontinuous and consisted of 7 stages separated by 1-minute recovery intervals. Stage durations of 3, 4 and 5 min were used in the different tests (IT3MIN, IT4MIN and IT5MIN). Mean values for VO2max were almost identical for IT1MIN (4.56+/-0.22 L x min(-1)), IT3MIN (4.60+/-0.23 L x min(-1)) and IT4MIN (4.60+/-0.21 L x min(-1)), while IT5MIN produced a significantly lower value (4.47+/-0.21 L x min(-1), p<0.05). There was no significant difference between protocols in peak post-exercise blood lactate concentration (approx 13 mmol x L(-1) in each case), but IT1MIN produced lower peak heart rates and higher respiratory exchange ratios. We conclude that with well trained rowing athletes discontinuous test protocols involving 7 stages of 3-4 minutes duration can provide valid measurements of VO2max.

Effects of four weeks intermittent hypoxia intervention on glucose homeostasis, insulin sensitivity, GLUT4 translocation, insulin receptor phosphorylation, and Akt activity in skeletal muscle of obese mice with type 2 diabetes

The purpose of this study was to investigate the recovery of muscle force generating capacity (FGC) of the lower limbs following a session of cycle exercise (CE). Fourteen male cyclists (mean +/- SD age 25 +/- 4 yrs and VO2max 65.8 +/- 5 ml x kg(-1)min(-1)) performed tests assessing lower limb muscle FGC at rest (pre-test), as well as 6 and 24 hrs following CE performed on a mechanically-braked cycle ergometer. The CE consisted of 30 min at a workload corresponding to the lactate (Dmax) threshold (+/-15 W), and four 60 s rides at 120% VO2max with one min rest between each ride. At the completion of the CE a 6 or 24 hr recovery period was initiated, after which, each subjects muscle FGC was measured. The analysis of lower limb muscle FGC included, (1) 6 s all-out cycle test; (2) a maximal isokinetic leg extension at 60, 120 and 180 degrees x s(-1); and (3) a maximal concentric squat jump. Statistical analysis showed that compared to pre-test levels, a significant reduction in both isokinetic peak torque at 60 degrees x s(-1) and isoinertial maximum force occurred after 6 hrs of recovery. Although not significant, reductions also occurred at 6 hrs of recovery in isokinetic peak torque at 120 and 180 degrees x s(-1), as well as maximum rate of force development (RFD) during the squat jumps. No significant differences were observed between isokinetic peak torque, maximum force or RFD pre-test and following the 24 hr recovery period, indicating these tests had returned to normal by this time. No significant differences were found between peak power (PP) during the 6 s cycle test, pre-test and following either 6 or 24 hrs of recovery. These findings confirm earlier research that maximal voluntary strength is reduced for at least 6 hours following exhaustive dynamic exercise. The reduction in muscle FGC should be considered when resistance training is scheduled after endurance exercise.