Effect of cycling cadence on contractile and neural properties of knee extensors.

PURPOSE: This study investigated the effect of prior prolonged cycling exercise performed at different cadences on subsequent neuromuscular characteristics. METHODS: Eight well-trained triathletes sustained 80% of their maximal aerobic power during 30 min at three cadences: the freely chosen cadence (FCC), FCC-20%, and FCC+20%. Maximal isometric and concentric (120 degrees x s(-1) and 240 degrees x s(-1)) torques were recorded before and after the exercise. Central activation, neural (M-wave), and contractile (isometric muscular twitch) parameters of quadriceps muscle were also analyzed by electrical stimulation of the femoral nerve. RESULTS: Reductions in maximal isometric (P < 0.01) and concentric torques at 120 degrees x s(-1) (P < 0.05) were found after exercise. Central activation levels fell significantly (P < 0.05) by 13-16% depending on the pedaling rate. Although the M-wave did not significantly change after exercise, the ratio EMG RMS/M-wave amplitude decreased significantly (P < 0.01) on both vastus lateralis and vastus medialis muscles for FCC-20% and FCC but not for FCC+20%. Significant decreases in maximal twitch tension (P < 0.01), maximal rate of twitch development (P < 0.01), and time to half relaxation (P < 0.01) were observed postexercise with no effect of cadence. CONCLUSIONS: These findings suggest that force reduction after prolonged cycling is attributable to both central and peripheral factors but is not influenced by the pedaling rate in a range of FCC +/- 20%.     

Vitamin and mineral supplementation and neuromuscular recovery after a running race

PURPOSE: This double-blind study investigated the effects of vitamin and mineral complex supplementation on the neuromuscular function of the knee-extensor muscles after a prolonged trail running race. METHODS: Twenty-two well-trained endurance runners took either placebo (Pl group) or vitamins and minerals (Vm group) for 21 d before the race and for 2 d after the race. Maximal voluntary contractions (MVC) and surface EMG activity of the vastus lateralis (VL) muscle were recorded before (pre) and 1 h (post), 24 h (post 24) and 48 h (post 48) after the race. Central activation ratio (CAR), neural (M-wave), and contractile (muscular twitch) properties of the quadriceps muscles were analyzed using electrical stimulation techniques. RESULTS: The knee-extensor MVC was significantly (P < 0.01) reduced after exercise for both groups (Vm: 36.5 +/- 3.0 %; Pl: 36.9 +/- 2.1%), but MVC recovery was greater for Vm than Pl after 48 h (11%, P < 0.05). The reduced MVC after exercise was associated with a significant reduction in maximal EMG normalized to the M-wave in VL muscle and in CAR for both groups. Characteristics of the muscular twitch were not significantly altered for either groups, whereas M-wave duration increased significantly (P < 0.05) after exercise. CONCLUSIONS: The reduction of MVC immediately after the race appeared to result from peripheral mechanisms such as a failure in muscle membrane excitation and, to a lesser extent, from reduced central activation. The cause of the depressed MVC 24 h after the race seemed to be located within the muscle itself. A dietary supplementation of a vitamin and mineral complex does not attenuate the loss of contractile function immediately after the running exercise, and it may accelerate the recovery of maximal force capacity.     

Why does knee extensor muscles torque decrease after eccentric-type exercise?

AIM: The purpose of this study was to re-examine central and peripheral origins of neuromuscular fatigue after a highly strenuous eccentric exercise of the knee extensor muscles (KE) using both voluntary/evoked contractions and electromyographic recordings (EMG). METHODS: Before, and 30 min after 15 min of intermittent one-logged downhill running, maximal percutaneous electrical stimulations (single twitch, 0.5 s tetanus at 20 Hz and 80 Hz) were applied to the femoral nerve of 10 male subjects. Electrically evoked superimposed twitches were delivered during isometric maximal voluntary contraction (MVC) to determine maximal voluntary activation (%VA). Vastus lateralis (VL), vastus medialis (VM) and biceps femoris (BF) EMG were recorded during MVC and quantified using the root mean square (RMS) value. M-wave characteristics were also determined. RESULTS: KE MVC and %VA decreased significantly with fatigue (-19.6+/-6.1%; P<0.001 and -7.8+/-6.6%; P<0.01, respectively). Peak tetanus tension at 20 and 80 Hz (P20 and P80, respectively) declined (P<0.001), concurrently with a decrement of the P20 x P80(-1) ratio (-37.3+/-16.6%; P<0.001). Antagonist muscle coactivation, RMS to M-wave peak-to-peak amplitude and MVC x P80(-1) ratios were unchanged after the fatiguing exercise. CONCLUSIONS: The results reveal that part of the large loss in MVC may have a central origin but most of the MVC decrement is due to the presence of low-frequency fatigue while possible contractile failure cannot be excluded.     

Short-term immobilization after eccentric exercise. Part I: contractile properties

PURPOSE: The purpose of this study was to examine the compound muscle action potential (M-wave) and evoked contractile properties of immobilized muscle after high-force eccentric exercise. We believed that changes in these variables would contribute to the enhanced recovery of maximal voluntary force observed after short-term immobilization of damaged muscle. We hypothesized that immobilization after eccentric exercise would result in an enhanced M-wave and a change in contractile properties toward characteristics of faster muscle fibers. METHODS: Twenty-five college-age males were matched according to force loss after 50 maximal eccentric contractions of the elbow flexors and placed into an immobilization (IMM, N = 12) or control (CON, N = 13) group. IMM had their arm immobilized at 90 degrees and secured in a sling during a 4-d treatment. Maximal isometric torque (MVC) was assessed at baseline and for 8 d after treatment. M-wave and evoked contractile properties of the muscle (twitch torque [TT], maximal rate of torque development [MRTD], time to peak torque [TPT], and one-half relaxation time [HRT]) were assessed at baseline and for the first 5 d after treatment. RESULTS: Immediately postexercise, MVC was reduced 43% and 42% in IMM and CON, respectively. Recovery of MVC was significantly greater in IMM during recovery (P < 0.05), 95% of baseline MVC compared with 83% in CON. M-wave was reduced 32%, and all contractile properties were altered immediately postexercise. M-wave, MRTD, TPT, and HRT were not significantly different between groups during recovery (P > 0.05). TT demonstrated enhanced recovery in IMM (P < 0.05). CONCLUSIONS: Short-term immobilization after eccentric exercise resulted in enhanced recovery of maximal voluntary force. However, enhanced force recovery cannot be explained by muscle activation and evoked contractile properties of the muscle.     

Time course of neuromuscular alterations during a prolonged running exercise

PURPOSE: This study investigated the time course of contractile and neural alterations of knee extensor (KE) muscles during a long-duration running exercise. METHODS: Nine well-trained triathletes and endurance runners sustained 55% of their maximal aerobic velocity (MAV) on a motorized treadmill for a period of 5 h. Maximal voluntary contraction (MVC), maximal voluntary activation level (%VA), and electrically evoked contractions (single and tetanic stimulations) of KE muscles were evaluated before, after each hour of exercise during short (10 min) interruptions, and at the end of the 5-h period. Oxygen uptake was also measured at regular intervals during the exercise. RESULTS: Reductions of MVC and %VA were significant after the 4th hour of exercise and reached -28% (P < 0.001) and -16% (P < 0.01) respectively at the end of the exercise. The reduction in MVC was highly correlated with the decline of %VA (r = 0.98, P < 0.001). M-wave was also altered after the fourth hour of exercise (P < 0.05) in both vastus lateralis and rectus femoris muscles. Peak twitch was potentiated at the end of the exercise (+18%, P = 0.01); 20- and 80-Hz maximal tetanic forces were not altered by the exercise. Oxygen uptake increased linearly during the running period (+18% at 5 h, P < 0.001). CONCLUSION: These findings suggest that KE maximal voluntary force generating capability is depressed in the final stages of a 5-h running exercise. Central activation failure and alterations in muscle action potential transmission were important mechanisms contributing to the impairment of the neuromuscular function during prolonged running.     

Electromyostimulation training effects on neural drive and muscle architecture

PURPOSE: The purpose of the study was to investigate the effect of 4 and 8 wk of electromyostimulation (EMS) training on both muscular and neural adaptations of the knee extensor muscles. METHODS: Twenty males were divided into the electrostimulated group (EG, N = 12) and the control group (CG, N = 8). The training program consisted of 32 sessions of isometric EMS over an 8-wk period. All subjects were tested at baseline (B) and retested after 4 (WK4) and 8 (WK8) wk of EMS training. The EMG activity and muscle activation obtained under maximal voluntary contractions (MVC) was used to assess neural adaptations. Torque and EMG responses obtained under electrically evoked contractions, muscle anatomical cross-sectional area (ACSA), and vastus lateralis (VL) pennation angle, both measured by ultrasonography imaging, were examined to analyze muscular changes. RESULTS: At WK8, knee extensor MVC significantly increased by 27% (P < 0.001) and was accompanied by an increase in muscle activation (+6%, P < 0.01), quadriceps muscle ACSA (+6%, P < 0.001), and VL pennation angle (+14%, P < 0.001). A significant increase in normalized EMG activity of both VL and vastus medialis (VM) muscles (+69 and +39%, respectively, P < 0.001) but not of rectus femoris (RF) muscle was also found at WK8. The ACSA of the VL, VM, and vastus intermedius muscles significantly increased at WK8 (5-8%, P < 0.001) but not at WK4, whereas no changes occurred in the RF muscle. CONCLUSION: We concluded that the voluntary torque gains obtained after EMS training could be attributed to both muscular and neural adaptations. Both changes selectively involved the monoarticular vastii muscles.     

Is eccentric exercise-induced torque decrease contraction type dependent?

PURPOSE: This study was designed to determine whether torque decrease following an acute eccentric exercise is contraction type dependent. METHODS: Ten active males performed an exercise session consisting of five sets of ten maximal eccentric muscle actions of the elbow flexors. Before and immediately after the exercise, maximal voluntary eccentric (-60 degrees.s-1; Ecc60), isometric (0 degrees.s-1; Iso) and concentric (60 degrees.s-1; Con60 and 240 degrees.s-1; Con240) torque were measured. In order to distinguish central from peripheral factors involved in torque decrement, activation level (twitch interpolation technique), myoelectrical activity (RMS) of biceps brachii, as well as electrically evoked M-wave and peak twitch torque (Pt) were recorded. RESULTS: The eccentric exercise induced a significant torque reduction (P < 0.01), whatever the muscular contraction type [mean (SD): -22.3 (8.1)% for Ecc60; -20.8 (11.2)% for Iso; -18.5 (6.1)% for Con60 and -12.5 (8.9)% for Con240]. Relative torque decrement was however significantly less for Con240 compared with Ecc60, Iso, and Con60 (P < 0.05). Torque decreases were associated with a reduction of both M-wave amplitude (P < 0.01) and Pt (P < 0.001), probably related to an impairment of the excitation-contraction coupling. Concurrently, activation level was reduced (P < 0.01), therefore indicating the occurrence of central fatigue, as also confirmed by RMS decreases for all the conditions (P < 0.05), except Con240. DISCUSSION: An acute eccentric exercise induced a significant voluntary maximal torque reduction during eccentric, isometric, and concentric muscle actions ascribed to both peripheral and central failure of force production capacity. It can be concluded that eccentric exercise-induced torque decrease is not contraction type dependent.     

Heterogeneous recruitment of quadriceps muscle portions and fibre types during moderate intensity knee-extensor exercise: effect of thigh occlusion

The involvement of quadriceps femoris muscle portions and fibre type recruitment was studied during submaximal knee-extensor exercise without and with thigh occlusion (OCC) and compared with responses during intense exercise. Six healthy male subjects performed 90-s of moderate exercise without (MOD; 29±4 W) and with thigh OCC, and moderate exercise followed by 90-s of intense exercise (HI; 65±8 W). Temperatures were continuously measured in m. vastus lateralis (VL), vastus medialis (VM) and rectus femoris (RF) and successive muscle biopsies were obtained from VL. During MOD, muscle temperature increase (Δ T _m) in RF was 0.52±0.09 °C, which was 57% and 73% higher ( P <0.05) than in VL and VM, respectively. During OCC, Δ T _m in RF was 0.39±0.05 °C, which was not different from VM but 54% higher ( P <0.05) than in VL. After MOD, muscle CP in slow twitch (ST) and fast twitch (FT) fibres was 81% and 91% of resting levels, respectively, with lower ( P <0.05) values after OCC (15% and 22%) and HI (24% and 13%). After MOD, OCC and HI, a total of 48%, 93% and 96% of the ST fibres had CP levels below mean-1 SD, respectively, with corresponding values for FT fibres being 41%, 89% and 100%, respectively. In conclusion, a heterogeneous recruitment of the quadriceps muscle portions and muscle fibres was observed during submaximal knee-extensor exercise, whereas recruitment pattern was homogenous during intense exercise. Thigh OCC caused an altered recruitment of fibres and muscle portions, suggesting a significant afferent response affecting the activation of fibres in the contracting muscles.     

Alteration of neuromuscular function in squash

The alteration in neuromuscular function of knee extensor muscles was characterised after a squash match in 10 trained players. Maximal voluntary contraction (MVC) and surface EMG activity of vastus lateralis (VL) and vastus medialis (VM) muscles were measured before and immediately after a 1-h squash match. M-wave and twitch contractile properties were analysed following single stimuli. MVC declined (280.5 ± 46.8 vs. 233.6 ± 35.4 N m, ?16%; P < 0.001) after the exercise and this was accompanied by an impairment of central activation, as attested by decline in voluntary activation (76.7 ± 10.4 vs. 71.3 ± 9.6%, ?7%; P < 0.05) and raw EMG activity of the two vastii (?17%; P < 0.05), whereas RMS/M decrease was lesser (VL: ?5%; NS and VM: ?12%; P = 0.10). In the fatigued state, no significant changes in M-wave amplitude (VL: ?9%; VM: ?5%) or duration were observed. Following exercise, the single twitch was characterised by lower peak torque (?20%; P < 0.001) as well as shorter half-relaxation time (?13%; P < 0.001) and reduced maximal rate of twitch tension development (?23%; P < 0.001) and relaxation (?17%; P < 0.05). A 1-h squash match play caused peripheral fatigue by impairing excitation–contraction coupling, whereas sarcolemmal excitability seems well preserved. Our results also emphasise the role of central activation failure as a possible mechanism contributing to the torque loss observed in knee extensors. Physical conditioners should consider these effects when defining their training programs for squash players.     

Effect of high-intensity intermittent cycling sprints on neuromuscular activity

High-intensity intermittent sprints induce changes in metabolic and mechanical parameters. However, very few data are available about electrical manifestations of muscle fatigue following such sprints. In this study, quadriceps electromyographic (EMG) responses to repeated all-out exercise bouts of short duration were assessed from maximal voluntary isometric contractions (MVC) performed before and after sprints. Twelve men performed ten 6-s maximal cycling sprints, separated by 30-s rest. The MVC were performed pre-sprints ( pre), post-sprints ( post), and 5 min post-sprints ( post5). Values of root-mean-square (RMS) and median frequency (MF) of vastus lateralis (VL) and vastus medialis (VM) were recorded during each MVC. During sprints, PPO decreased significantly in sprints 8, 9, and 10, compared to sprint 1 (- 8 %, - 10 %, and - 11 %, respectively, p < 0.05). Significant decrements were found in MVC post (- 13 %, p < 0.05) and MVC post5 (- 10.5 %, p < 0.05) compared to MVC pre. The RMS value of VL muscle increased significantly after sprints (RMS pre vs. RMS post: + 15 %, p < 0.05). Values of MF decreased significantly in both VL and VM after sprints. In conclusion, our results indicate that the increase in quadriceps EMG amplitude following high-intensity intermittent short sprints was not sufficient to maintain the required force output. The concomitant decrease in frequency components would suggest a modification in the pattern of muscle fiber recruitment, and a decrease in conduction velocity of active fibers.     

The effects of a prolonged running exercise on strength characteristics

The aim of this study was to examine concentric, isometric, and eccentric strength reductions in the quadriceps muscle following a prolonged running exercise. Before and after a 2 h run (28.4+/-1.4 km) peak torque (PT) of the knee extensors at angular velocities of -120, -90, -60, 0, 60, 120, 180, 240 degrees x s(-1) using an isokinetic dynamometer, electromyographic (EMG) activity of the vastus lateralis (VL) and vastus medialis (VM) muscles and height of a counter movement jump were recorded in twelve well-trained triathletes. Counter movement jump performances decreased by 10% and PT values were all significantly lower (p < 0.01) at each angular velocity following the run. The torque loss was significantly (p < 0.01) greater under eccentric contractions (from 18 to 21%) than under concentric ones (from 11 to 14%). EMG activity (RMS) was lower in both VL and VM muscles after the 2 h run but no difference existed in RMS losses between concentric and eccentric contractions. The present results demonstrate that 1) a prolonged running exercise more greatly affects eccentric force production in the quadriceps muscle, and 2) this specificity seems to be due to an impairment of the muscular contractile mechanism rather than a modification to the neural input.     

Aerobic and anaerobic power characteristics of off-road cyclists

PURPOSE: The purpose of this study was to describe the relationship between anaerobic power at different pedaling frequencies (including the optimal cadence) and aerobic power in off-road cyclists (CYC; N = 25) and sports students, who did not perform specific cycle exercise more than two times per week (CON; N = 60). METHODS: To describe the aerobic power, we measured the maximal power output (W(max)) and the power output at the fixed lactate threshold at 4 mmol x L(-1) (W(L4)) obtained during a maximal aerobic power cycling test. To describe anaerobic power output, we measured the average power output (IsoW(mean)) over a range from 50 to 140 rpm by using a 10-s sprint on an isokinetic cycle ergometer. RESULTS: For the 10-s anaerobic test, CON and CYC showed a peak power output (IsoW(peak)) of 13.3 +/- 1.4 and 14.9 +/- 1.1 W x kg(-1), respectively. IsoW(peak) corresponded to an optimal cadence of 100 +/- 9.3 rpm for CON and 100 +/- 8.7 rpm for CYC. There was a significant difference (P < 0.001) in the W(max):IsoW(peak) (W(aerobic):W(anaerobic)) ratio between CON (32 +/- 4.5%) and CYC (38 +/- 3.9%). Significant differences among group means were identified using an ANOVA test and a post hoc analysis. The off-road cyclists showed a significantly higher IsoW(mean) at all pedaling frequencies and at the optimal cadence (P < 0.01). There was a modest relationship between W(max) and IsoW(peak) in both groups (CON r = 0.53; CYC r = 0.64; P < 0.01). CONCLUSION: Anaerobic power values are important components associated with cycle performance in both noncyclists and off-road cyclists. However, the results of the present study demonstrated the usefulness of the power index in the physiological evaluation of off-road cyclists, as it gives information on the proportion of aerobic to anaerobic energy contribution.     

The effect of Q Factor on gross mechanical efficiency and muscular activation in cycling

Unexplored in scientific literature, Q Factor describes the horizontal width between bicycle pedals and determines where the foot is laterally positioned throughout the pedal stroke. The aim of the study was to determine whether changing Q Factor has a beneficial effect upon cycling efficiency and muscular activation. A total of 24 trained cyclists (11 men, 13 women; VO_2max 57.5 ml·kg/min ± 6.1) pedaled at 60% of peak power output for 5 min at 90 rpm using Q Factors of 90, 120, 150, and 180 mm. Power output and gas were collected and muscular activity of the gastrocnemius medialis (GM), tibialis anterior (TA), vastus medialis (VM), and vastus lateralis (VL) measured using surface electromyography. There was a significant increase (P < 0.006) in gross mechanical efficiency (GME) for 90 and 120 mm (both 19.38%) compared with 150 and 180 mm (19.09% and 19.05%), representing an increase in external mechanical work performed of approximately 4–5 W (1.5–2.0%) at submaximal power outputs. There was no significant difference in the level of activity or timing of activation of the GM, TA, VM, and VL between Q Factors. Other muscles used in cycling, and possibly an improved application of force during the pedal stroke may play a role in the observed increase in GME with narrower Q Factors.     

Fatigue and recovery after high-intensity exercise. Part II: Recovery interventions

The purpose of this study was to determine the effect of three types of recovery intervention to neuromuscular function after high-intensity uphill running exercise. The 20-min recovery interventions were (i) passive, (ii) active (running at 50 % of maximal aerobic speed), and (iii) low-frequency electromyostimulation. Evoked twitch and maximal voluntary contractions of knee extensor muscles (KE) and EMG of the vastus lateralis and vastus medialis were analysed immediately after the exercise, 10 min after the end of the recovery periods, and 65 min after the exercise (Post65). An all-out running test was also performed 80 min after the end of the fatiguing exercise. No significant differences were noted in any measured parameters but a tendency to a better performance during the all-out test was found after the electromyostimulation intervention (297.5 +/- 152.4 s vs. 253.6 +/- 117.1 s and 260.3 +/- 105.8 s after active and passive recovery, p = 0.13 and p = 0.12, respectively). At Post65, isometric maximal voluntary contraction torque did not return to the pre-exercise values (279.7 +/- 86.5 vs. 298.7 +/- 92.6 Nm, respectively; p < 0.05). During recovery, electrically evoked twitch was characterized by an increase of peak torque, maximal rate of force development and relaxation (+ 24 - 33 %; p < 0.001) but these values were still lower at Post65 than pre-exercise. Amplitude and surface of the M-wave decreased during recovery. These results show that the recovery of the voluntary force-generating capacity of KE after an intermittent high-intensity uphill running exercise do not depend on the type of recovery intervention tested here. It can also be concluded that the recovery of twitch contractile properties does not necessarily follow that of maximal muscle strength.     

Muscle conduction velocity,strength, neural activity,and morphological changes after eccentric and concentric training

This study compared the effects of concentric and eccentric training on neuromuscular adaptations in young subjects. Twenty‐two men and women were assigned to one of two groups: concentric (CON, n = 11) and eccentric (ECC, n = 11) training. Training consisted of 6 weeks of isokinetic exercise, performed twice weekly, starting with two sets of eight repetitions, and progressing to five sets of 10 repetitions. Subjects were tested in strength variables [concentric, eccentric, and isometric peak torque (PT), and rate of force development (RFD)], muscle conduction velocity (CV), neuromuscular activity, vastus lateralis (VL) muscle thickness, and echo intensity as determined by ultrasonography. There were similar increases in the concentric and eccentric PTs in both the CON and ECC groups (P < 0.01), but only the ECC group showed an increase in isometric PT (P < 0.001). Similarly, both groups exhibited increased VL muscle thickness, CV, and RFD, and reduced VL echo intensity (P < 0.05). Significant correlations were observed among the relative changes in the neuromuscular outcomes and training variables (e.g., total work, average PT) (r = 0.68–0.75, P < 0.05). The results showed that both training types similarly improved dynamic PT, CV, RFD, and muscle thickness and quality during the early weeks of training.     

Eccentric exercise in coronary patients: central hemodynamic and metabolic responses

PURPOSE: With lengthening (eccentric) muscle contractions, the magnitude of locomotor-muscle mass and strength increase has been demonstrated to be greater compared with shortening (concentric) muscle contractions. In healthy subjects, energy demand and heart rate responses with eccentric exercise are small relative to the amount of muscle force produced. Thus, eccentric exercise may be an attractive alternative to resistance exercise for patients with limited cardiovascular exercise tolerance. METHODS: We tested the cardiovascular tolerance of eccentric exercise in 13 coronary patients (ages 40-66) with preserved and/or mild reduced left ventricular function. Patients were randomly assigned to either an eccentric (ECC; N = 7) or a concentric (CON; N = 6) training group and trained for 8 wk. Training workload was increased progressively (from week 1 to 5) to an intensity equivalent to 60% [OV0312]O(2peak). RESULTS: On average, maximum power output achieved with ECC was fourfold compared with CON (357 +/- 96 W vs 97 +/- 21 W; P < 0.005), whereas measures of oxygen uptake and blood lactate were significantly lower (P < 0.05 each), and ratings of perceived exertion were similar for ECC and CON. During a 20-min session of ECC and CON, central hemodynamics was measured by means of right heart catheterization. During ECC, responses of mean arterial blood pressure, systemic vascular resistance, pulmonary capillary pressure, cardiac index, and stroke work of the left ventricle on average were in the normal range of values and similar to those observed during CON. Compared with baseline, after 8 wk of training, echocardiographic left ventricular function was unchanged. CONCLUSION: The results indicate uncoupling of skeletal muscle load and cardiovascular stress during ECC. For low-risk patients with coronary heart disease without angina, inducible ischemia, or left ventricular dysfunction, ECC can be recommended as a safe new approach to perform high-load muscular exercise training with minimal cardiovascular stress.     

Effects of prior exercise on force-velocity test performance and quadriceps EMG

This study investigated the effects of prior exercise on performance during a subsequent force-velocity (FV) exercise test. After determination of the individual maximal aerobic power (MAP) during maximal graded exercise testing, fifteen trained male subjects (age: 25 +/- 3 y) were randomly assigned to perform the FV exercise test without prior exercise (NPE) or preceded by prior exercise (PE) (10 min at 60 % of MAP, followed after 1-min rest interval by four intervals of 30-s cycling at 100 % MAP with 15-s rest intervals, then 10 min recovery). Blood samples were drawn at rest, and then for each work load at the 3rd minute of recovery. Skin temperature (T (sk)) from the rectus femoris and heart rate (HR) were measured continuously during prior exercise, the FV test, and during the 5-min recovery period at the end of each FV test. The Root Mean Square (RMS) of the surface electromyogram (EMG) signals obtained from the vastus lateralis (VL), vastus medialis (VM), and rectus femoris (RF) were calculated during each sprint for each FV test. The lactate increase for each load (deltaLa) during the FV test was significantly less following PE than NPE. However, the lactate concentration (La) was significantly higher in the FV test following PE than NPE. There was an improvement in power output during the first two sprints (2 and 4 kg) following PE compared to NPE. There was also a more pronounced decrease in VL, VM, and RF RMS in PE compared to NPE. Our results showed that the first few sprints may provide sufficient prior exercise for the FV test. The higher lactate concentration following PE than NPE, despite no difference in maximum power, suggests that a large lactate accumulation may not be detrimental to FV test performance. However, a greater lactate concentration and T(sk) may be associated with a decrease in RMS.     

A new pedaling design: the Rotor--effects on cycling performance

PURPOSE: To assess the effects of the Rotor (ROT), a new pedaling system that makes each pedal independent from the other so that cranks are no longer fixed at 180 degrees, on endurance cycling performance. METHODS: Following a randomized design, eight subjects (noncyclists; age (mean +/- SEM): 22 +/- 1 yr; VO(2max): 51.8 +/- 1.0 mL x kg(-1) x min(-1)) performed two bicycle-ergometer tests on separate days, one with the conventional pedaling system (CON) and the other one with ROT. Starting at 75 W, the power output was increased by 25 W at 3-min intervals until volitional exhaustion. Gas exchange parameters and blood lactate were measured for every 3-min interval. RESULTS: At exercise intensities between 60 and 90% VO(2max), delta efficiency (DE) was significantly higher in ROT than in CON (24.4 +/- 1.9% vs 21.1 +/- 1.1%, respectively). CONCLUSIONS: Although more research is needed, especially with trained riders, the Rotor system might improve delta efficiency during endurance cycling. Other performance determinants VO(2max), maximal power output) do not seem to be changed compared with the conventional system.     

Eccentric cycling is more efficient in reducing fat mass than concentric cycling in adolescents with obesity

The benefits of eccentric (ECC) training on fat mass (FM) remain underexplored. We hypothesized that in obese adolescents, ECC cycling training is more efficient for decreasing whole‐body FM percentage compared to concentric (CON) performed at the same oxygen consumption (VO₂). Twenty‐four adolescents aged 13.4 ± 1.3 years (BMI > 90th percentile) were randomized to ECC or CON. They performed three cyclo‐ergometer sessions per week (30 min per session) for 12 weeks: two habituation, 5 at 50% VO_2peak, and 5 at 70% VO_2peak. Anthropometric measurements, body composition, maximal incremental CON tests, strength tests, and blood samples were assessed pre‐ and post‐training. Whole‐body FM percentage decreased significantly after compared to pretraining in both groups, though to a larger extent in the ECC group (ECC: ?10% vs CON: ?4.2%, P < 0.05). Whole‐body lean mass (LM) percentage increased significantly in both groups after compared to pretraining, with a greater increase in the ECC group (ECC: 3.8% vs CON: 1.5%, P <0.05). The improvements in leg FM and LM percentages were greater in the ECC group (?6.5% and 3.0%, P = 0.01 and P < 0.01). Quadriceps isometric and isokinetic ECC strength increased significantly more in the ECC group (28.3% and 21.3%, P < 0.05). Both groups showed similar significant VO_2peak improvement (ECC: 15.4% vs CON: 10.3%). The decrease in homeostasis model assessment of insulin resistance index was significant in the ECC group (?19.9%). In conclusion, although both ECC and CON cycling trainings are efficient to decrease FM, ECC induces greater FM reduction, strength gains, and insulin resistance improvements and represents an optimal modality to recommend for obese adolescents.