Optimal pedalling velocity characteristics during maximal and submaximal cycling in humans

The aim of this study was to compare optimal pedalling velocities during maximal (OVM) and submaximal (OVSM) cycling in human, subjects with different training backgrounds. A group of 22 subjects [6 explosive (EX), 6 endurance (EN) and 10 non-specialised subjects] sprint cycled on a friction-loaded ergometer four maximal sprints lasting 6 s each followed by five 3-min periods of steady-state cycling at 150 W with pedalling frequencies varying from 40 to 120 rpm. The OVM and OVSM were defined as the velocities corresponding to the maximal power production and the lowest oxygen consumption, respectively. A significant linear relationship (r2 = 0.52, P < 0.001) was found between individual OVM [mean 123.1 (SD 11.2) rpm] and OVSM [mean 57.0 (SD 4.9) rpm, P < 0.001] values, suggesting that the same functional properties of leg extensor muscles influence both OVM and OVSM. Since EX was greater than EN in both OVM and OVSM (134.3 compared to 110.9 rpm and 60.8 compared to 54.0 rpm, P < 0.01 and P < 0.05, respectively) it could be hypothesised that the distribution of muscle fibre type plays an important role in optimising both maximal and submaximal cycling performance.     

EMG versus oxygen uptake during cycling exercise in trained and untrained subjects.

The aim of this study was to test the hypothesis that bicycle training may improve the relationship between the global SEMG energy and VO2. We already showed close adjustment of the root mean square (RMS) of the surface electromyogram (SEMG) to the oxygen uptake (VO2) during cycling exercise in untrained subjects. Because in these circumstances an altered neuromuscular transmission which could affect SEMG measurement occurred in untrained individuals only, we searched for differences in the SEMG vs. VO2 relationship between untrained subjects and well-trained cyclists. Each subject first performed an incremental exercise to determine VO2max and the ventilatory threshold, and second a constant-load threshold cycling exercise, continued until exhaustion. SEMG from both vastus lateralis muscles was continuously recorded. RMS was computed. M-Wave was periodically recorded. During incremental exercise: (1) a significant non-linear positive correlation was found between RMS increase and VO2 increase in untrained subjects, whereas the relationship was best fitted by a straight line in trained cyclists; (2) the RMS/VO2 ratio decreased progressively throughout the incremental exercise, its decline being significantly and markedly accentuated in trained cyclists; (3) in untrained subjects, significant M-wave alterations occurred at the end of the trial. These M-wave alterations could explain the non-linear RMS increase in these individuals. During constant-load exercise: (1) after an initial increase, the VO2 ratio decreased progressively to reach a plateau after 2 min of exercise, but no significant inter-group differences were noted; (2) no M-wave changes were measured in the two groups. We concluded that the global SEMG energy recorded from the vastus lateralis muscle is a good estimate of metabolic energy expenditure during incremental cycling exercise only in well-trained cyclists.     

Time-of-day effects on myoelectric and mechanical properties of muscle during maximal and prolonged isokinetic exercise

The aim of this study was to examine the time-of-day (TOD) effects in myoelectric and mechanical properties of muscle during a maximal and prolonged isokinetic exercise. Twelve male subjects were asked to perform 50 maximal voluntary contractions (MVC) of the knee extensor muscles at a constant angular velocity of 2.09 rad . sec(-1), at 06 : 00 and 18 : 00 h. Torque and electromyographic (EMG) parameters were recorded for each contraction, and the ratio between these values was calculated to evaluate variations of the neuromuscular efficiency (NME) with fatigue and with TOD. The results indicated that maximal torque values (T(45)Max) was significantly higher (7.73%) in the evening than in the morning (p<0.003). The diurnal variation in torque decrease was used to define two phases. During the first phase (1st to the 26th repetition), torque values decreased fast and values were higher in the evening than in the morning, and during the second phase (27th to the 50th repetition), torque decreased slightly and reached a floor value that appeared constant with TOD. The EMG parameters (Root Mean Square; RMS) were modified with fatigue, but were not TOD dependent. The NME decrease-significantly with fatigue, showing that peripheral factors were mainly involved in the torque decrease. Furthermore, NME decrease was greater at 18 : 00 than at 06 : 00 h for the vastus medialis (p<0.05) and the vastus lateralis muscles (p<0.002), and this occurred during the first fatigue phase of the exercise. In conclusion, the diurnal variation of the muscle fatigue observed during a maximal and prolonged isokinetic exercise seems to reflect on the muscle, with a greater contractile capacity but a higher fatigability in the evening compared to the morning.     

Bivariate optimization of pedalling rate and crank arm length in cycling

The contribution of this paper is a bivariate optimization of cycling performance. Relying on a biomechanical model of the lower limb, a cost function derived from the joint moments developed during cycling is computed. At constant average power, both pedalling rate (i.e. rpm) and crank arm length are systematically varied to explore the relation between these variables and the cost function. A crank arm length of 170 mm and pedalling rate of 100 rpm correspond closely to the cost function minimum. In cycling situations where the rpm deviates from 100 rpm, however, crank arms of length other than 170 mm yield minimum cost function values. In addition, the sensitivity of optimization results to both increased power and anthropometric parameter variations is examined. At increased power, the cost function minimum is more strongly related to the pedalling rate, with higher pedalling rates corresponding to the minimum. Anthropometric parameter variations influence the results significantly. In general it is found that the cost function minimum for tall people occurs at longer crank arm lengths and lower pedalling rates than the length and rate for short people.     

The effect of saddle position on maximal power output and moment generating capacity of lower limb muscles during isokinetic cycling

Saddle position affects mechanical variables during submaximal cycling, but little is known about its effect on mechanical performance during maximal cycling. Therefore, this study relates saddle position to experimentally obtained maximal power output and theoretically calculated moment generating capacity of hip, knee and ankle muscles during isokinetic cycling. Ten subjects performed maximal cycling efforts (5 s at 100 rpm) at different saddle positions varying ± 2 cm around the in literature suggested optimal saddle position (109% of inner leg length), during which crank torque and maximal power output were determined. In a subgroup of 5 subjects, lower limb kinematics were additionally recorded during submaximal cycling at the different saddle positions. A decrease in maximal power output was found for lower saddle positions. Recorded changes in knee kinematics resulted in a decrease in moment generating capacity of biceps femoris, rectus femoris and vastus intermedius at the knee. No differences in muscle moment generating capacity were found at hip and ankle. Based on these results we conclude that lower saddle positions are less optimal to generate maximal power output, as it mainly affects knee joint kinematics, compromising mechanical performance of major muscle groups acting at the knee.     

EMG recurrence quantifications in dynamic exercise

This study was designed to evaluate the suitability of nonlinear recurrence quantification analysis (RQA) in assessing electromyograph (EMG) signals during dynamic exercise. RQA has been proven to be effective in analyzing nonstationary signals. The subject group consisted of 19 male patients diagnosed with low back pain. EMG signals were recorded from left and right paraspinal muscles during isoinertial exercise both before and after 12 weeks of regimented physical therapy. Autorecurrence analysis was performed between the left and right EMG signals individually, and cross-recurrence analysis was performed on the left-right EMG pairs. Spectral analysis of the EMG signals was employed as an independent, objective measure of fatigue. Increase in the RQA variable % determinism during the 90-s dynamic tests was found to be a good marker for fatigue. Before physical therapy, this nonlinear marker revealed simultaneous increases in motor unit recruitment within each pool and between left and right pools. After physical therapy, the motor unit recruitment was less within and between pools, indicative of increased fatigue resistance. Finally, fatigue resistance (less increase in % determinism) correlated well with subjective scores of pain relief. Taken together, these latter results indicate that recurrence analysis may be useful in charting the efficacy of a specific exercise therapy program in reducing low back pain by elevating the fatigue threshold.     

Plasmatic markers of muscular stress in isokinetic exercise

In this paper we examined the variations of plasmatic concentrations of hypoxanthine and xanthine, and their relation with other important indicators of muscular stress creatine-kinase (CK), myoglobin, uric acid, leucocytes, in prolonged, isokynetic physical exercise, performed in a concentric mode at different joint excursion. Twenty healthy male subjects performed isokinetic exercises in concentric-concentric mode, with joint excursion of 30, 60, 90 deg/sec. Blood samples were drawn at rest, immediately after exercise and after 45 min of recovery. The plasmatic concentration of hypoxanthine increased at the end of physical exercise, compared to the rest value of about 1,5 micromol/L, up to a level of greater than 19 micromol/L; the values were higher after a period of recovery of 45 min and the increase varies considerably according to the type of exercise that was performed. Myoglobin has a slight but sensible increment too, with the same trend as hypoxanthine, while CK increase without correlation to the type of exercises. The relation with other indicators of muscular activity demonstrates that in none of the different isokinetic exercises, performed at concentric mode, was there ultrastructural damage, while it is possible to come across a considerable metabolic stress, which is dissimilar in the different kinds of exercises. The results suggest that hypoxanthine can be useful in monitoring the effectiveness of a work load and the metabolic stress consequences on the muscle tissue in training or rehabilitation programs. The results also suggest that even myoglobin, at small concentrations, can have the same function.     

A non-MVC EMG normalization technique for the trunk musculature: Part 1. Method development.

Normalization of muscle activity has been commonly used to determine the amount of force exerted by a muscle. The most widely used reference point for normalization is the maximum voluntary contraction (MVC). However, MVCs are often subjective, and potentially limited by sensation of pain in injured individuals. The objective of the current study was to develop a normalization technique that predicts an electromyographic (EMG) reference point from sub-maximal exertions. Regression equations predicting maximum exerted trunk moments were developed from anthropometric measurements of 120 subjects. In addition, 20 subjects performed sub-maximal and maximal exertions to determine the necessary characteristic exertions needed for normalization purposes. For most of the trunk muscles, a highly linear relationship was found between EMG muscle activity and trunk moment exerted. This analysis determined that an EMG-moment reference point can be obtained via a set of sub-maximal exertions in combination with a predicted maximal exertion (expected maximum contraction or EMC) based upon anthropometric measurements. This normalization technique overcomes the limitations of the subjective nature for the MVC method providing a viable assessment method of individuals with a low back injury or those unwilling to exert an MVC as well as could be extended to other joints/muscles.     

A method for biomechanical analysis of bicycle pedalling

This paper reports a new method, which enables a detailed biomechanical analysis of the lower limb during bicycling. The method consists of simultaneously measuring both the normal and tangential pedal forces, the EMGs of eight leg muscles, and the crank arm and pedal angles. Data were recorded for three male subjects of similar anthropometric characteristics. Subjects rode under different pedalling conditions to explore how both pedal forces and pedalling rates affect the biomechanics of the pedalling process. By modelling the leg-bicycle as a five bar linkage and driving the linkage with the measured force and kinematic data, the joint moment histories due to pedal forces only (i.e. no motion) and motion only (i.e. no pedal forces) were generated. Total moments were produced by superimposing the two moment histories. The separate moment histories, together with the pedal forces and EMG results, enable a detailed biomechanical analysis of bicycle pedalling. Inasmuch as the results are similar for all three subjects, the analysis for one subject is discussed fully. One unique insight gained via this new method is the functional role that individual leg muscles play in the pedalling process.     

Pacing pattern in a 30-minute maximal cycling test

The purpose of this study was to investigate the pacing pattern and associated physiological effects in competitive cyclists who performed a 30-minute maximal cycling test. Measurements included oxygen uptake (V O2), heart rate (HR), blood lactate concentration (BLC), rating of perceived exertion (RPE), and work rate in watts. Twelve well-trained amateur cyclists (seven men and five women) whose mean age was 32.4 +/- 8.6 years participated in this study. They performed a 30-minute self-paced maximal cycling test using their own performance road bike attached to a CompuTrainer Pro, which allowed the assessment of work rate (W). During the test, work rate, V O2, and HR were measured every 30 seconds. Subjects' BLC and RPE were obtained every 5 minutes. Results indicate that no significant differences existed across three 10-minute periods for work rate, HR, or V O2. However, RPE at 30 minutes was significantly greater than RPE at 10 and 20 minutes (both p < 0.05). The RPE at 20 minutes was also greater than the RPE at 10 minutes (p < 0.01). Work rate remained relatively constant, with minimal fluctuations occurring throughout the test except for a surge during the final 30 seconds of the test. The associated V O2 was fairly constant over time, whereas HR rose linearly and gradually. It was concluded that pacing in a 30-minute maximal exercise bout performed in the laboratory in experienced cyclists varies minimally until the last 30 seconds. Knowledge of pacing strategy and the linked physiological responses may be helpful to exercise scientists in optimizing performance in the endurance athlete.     

EMG median power frequency in an exhausting exercise

EMG median power frequency of the calf muscles was investigated during an exhausting treadmill exercise. This exercise was an uphill run, the average endurance time was 1.5 min. Median power frequency of the calf muscles declined by more than 10% during this exercise. In addition EMG median power frequency of isometric contractions of the same muscles was measured before and in one minute intervals for 10 min after this run. Immediately after the run isometric median power frequency had declined by less than 5% for the soleus muscle, more than 10% for the gastrocnemius medialis and gastrocnemius lateralis muscles. In the 10 min following exercise the isometric median power frequency increased to pre-execise levels. Maybe the median power frequency shift to lower frequencies during dynamic exercise can be interpreted as a sign of local muscle fatigue.     

Relationships between muscle lactate accumulation and surface EMG activities during isokinetic contractions in man

In order to investigate the relationship between metabolic state and myoelectrical activity in working muscle during short term intense exercise, eleven healthy males performed isokinetic knee extensions at an angular velocity of 180 deg X sec-1 for 30 and 60 s. The median frequency (MF) of the surface electromyogram (EMG) recorded from vastus lateralis was decreased while the time lag of torque production after the onset of electrical activity (EMD) was increased during exercise. These changes (MF and EMD) corresponded well to muscle lactate accumulation in the same muscle. Over the exercise period, the integrated EMG/knee extension peak torque ratio (E/T ratio) was increased, which indicated a decrease in the efficiency of electrical activity. It was concluded that the changes in the frequency components of the EMG and in the contractile property of the muscle during short term intense exercise correlated with lactate accumulation in the identical muscle, and that the decrease in efficiency of the electrical activity in the muscle suggested peripheral fatigue.     

The influence of body position on maximal performance in cycling

Six healthy male subjects performed a 3-min supramaximal test in four different cycling positions: two with different trunk angles and two with different saddle-tube angles. Maximal power output and maximal oxygen uptake (VO2max) were measured. Maximal power output was significantly higher in a standard sitting (SS, 381 W, SD 49) upright position compared to all other positions: standard racing (SR, 364 W, SD 49), recumbent backwards (RB, 355 W, SD 44) and recumbent forwards (RF, 341 W, SD 54). Although VO2max was also highest in SS (4.31 l.min-1, SD 0.5) upright position, the differences in VO2max were not significant (SR, 4.2 l.min-1, SD 0.53; RB, 4.17 l.min-1, SD 0.58; RF, 4.11 l.min-1, SD 0.66). It is concluded that (supra)maximal tests on a cycle ergometer should be performed in a sitting upright position and not in a racing position. In some cases when cycling on the road, higher speeds can be attained when sitting upright. This is especially true when cycling uphill when high power must be generated to overcome gravity but the road speed, and hence the power required to overcome air resistance, is relatively low.     

Factors in maximal power production and in exercise endurance relative to maximal power

The relationship of muscle fiber type and mass to maximal power production and the maintenance of power (endurance time to exhaustion) at 36%, 55%, and 73% of maximal power was investigated in 18 untrained but physically active men. Power output was determined at constant pedalling rate (60 rev.min-1) on a cycle ergometer instrumented with force transducers and interfaced with a computer. Maximal power was determined for each subject as the highest one-revolution average power. Fat-free mass was determined by hydrostatic weighing, fat-free thigh volume by water displacement and skinfold measurement, and percentage and area of type II fibers from biopsy specimens taken from the vastus lateralis. Maximal power averaged 771 +/- 149 W with a range of 527-1125 W. No significant correlations were found among percentage of type II fibers, relative area of type II fibers, or fat-free thigh volume and maximal power or endurance times to exhaustion at any percentage of maximal power. Weak but significant relationships were found for fat-free mass with both maximal power (r = 0.57) and endurance time at 73% of maximal power (r = -0.47). These results show maximal power to be more dependent on factors related to body size than muscle-fiber characteristics. The low correlations for so many of the relationships, however, suggest that individuals employ either different combinations of these factors or utilize other strategies for the generation of high power.     

Effects on the crank torque profile when changing pedalling cadence in level ground and uphill road cycling

Despite the importance of uphill cycling performance during cycling competitions, there is very little research investigating uphill cycling, particularly concerning field studies. The lack of research is partly due to the difficulties in obtaining data in the field. The aim of this study was to analyse the crank torque in road cycling on level and uphill using different pedalling cadences in the seated position. Seven male cyclists performed four tests in the seated position (1) on level ground at 80 and 100 rpm, and (2) on uphill road cycling (9.25% grade) at 60 and 80 rpm.The cyclists exercised for 1 min at their maximal aerobic power. The bicycle was equipped with the SRM Training System (Schoberer, Germany) for the measurement of power output (W), torque (Nm), pedalling cadence (rpm), and cycling velocity (km h(-1)). The most important finding of this study indicated that at maximal aerobic power the crank torque profile (relationship between torque and crank angle) varied substantially according to the pedalling cadence and with a minor effect according to the terrain. At the same power output and pedalling cadence (80 rpm) the torque at a 45 degrees crank angle tended (p < 0.06) to be higher (+26%) during uphill cycling compared to level cycling. During uphill cycling at 60 rpm the peak torque was increased by 42% compared with level ground cycling at 100 rpm.When the pedalling cadence was modified, most of the variations in the crank torque profile were localised in the power output sector (45 degrees to 135 degrees).     

Dietary nitrate reduces maximal oxygen consumption while maintaining work performance in maximal exercise

The anion nitrate—abundant in our diet—has recently emerged as a major pool of nitric oxide (NO) synthase-independent NO production. Nitrate is reduced stepwise in vivo to nitrite and then NO and possibly other bioactive nitrogen oxides. This reductive pathway is enhanced during low oxygen tension and acidosis. A recent study shows a reduction in oxygen consumption during submaximal exercise attributable to dietary nitrate. We went on to study the effects of dietary nitrate on various physiological and biochemical parameters during maximal exercise. Nine healthy, nonsmoking volunteers (age 30 ± 2.3 years, VO_2max 3.72 ± 0.33 L/min) participated in this study, which had a randomized, double-blind crossover design. Subjects received dietary supplementation with sodium nitrate (0.1 mmol/kg/day) or placebo (NaCl) for 2 days before the test. This dose corresponds to the amount found in 100–300 g of a nitrate-rich vegetable such as spinach or beetroot. The maximal exercise tests consisted of an incremental exercise to exhaustion with combined arm and leg cranking on two separate ergometers. Dietary nitrate reduced VO_2max from 3.72 ± 0.33 to 3.62 ± 0.31 L/min, P < 0.05. Despite the reduction in VO_2max the time to exhaustion trended to an increase after nitrate supplementation (524 ± 31 vs 563 ± 30 s, P = 0.13). There was a correlation between the change in time to exhaustion and the change in VO_2max (R² = 0.47, P = 0.04). A moderate dietary dose of nitrate significantly reduces VO_2max during maximal exercise using a large active muscle mass. This reduction occurred with a trend toward increased time to exhaustion implying that two separate mechanisms are involved: one that reduces VO_2max and another that improves the energetic function of the working muscles.     

Chronic intermittent hypoxia and incremental cycling exercise independently depress muscle in vitro maximal Na+-K+-ATPase activity in well-trained athletes.

Athletes commonly attempt to enhance performance by training in normoxia but sleeping in hypoxia [live high and train low (LHTL)]. However, chronic hypoxia reduces muscle Na(+)-K(+)-ATPase content, whereas fatiguing contractions reduce Na(+)-K(+)-ATPase activity, which each may impair performance. We examined whether LHTL and intense exercise would decrease muscle Na(+)-K(+)-ATPase activity and whether these effects would be additive and sufficient to impair performance or plasma K(+) regulation. Thirteen subjects were randomly assigned to two fitness-matched groups, LHTL (n = 6) or control (Con, n = 7). LHTL slept at simulated moderate altitude (3,000 m, inspired O(2) fraction = 15.48%) for 23 nights and lived and trained by day under normoxic conditions in Canberra (altitude approximately 600 m). Con lived, trained, and slept in normoxia. A standardized incremental exercise test was conducted before and after LHTL. A vastus lateralis muscle biopsy was taken at rest and after exercise, before and after LHTL or Con, and analyzed for maximal Na(+)-K(+)-ATPase activity [K(+)-stimulated 3-O-methylfluorescein phosphatase (3-O-MFPase)] and Na(+)-K(+)-ATPase content ([(3)H]ouabain binding sites). 3-O-MFPase activity was decreased by -2.9 +/- 2.6% in LHTL (P < 0.05) and was depressed immediately after exercise (P < 0.05) similarly in Con and LHTL (-13.0 +/- 3.2 and -11.8 +/- 1.5%, respectively). Plasma K(+) concentration during exercise was unchanged by LHTL; [(3)H]ouabain binding was unchanged with LHTL or exercise. Peak oxygen consumption was reduced in LHTL (P < 0.05) but not in Con, whereas exercise work was unchanged in either group. Thus LHTL had a minor effect on, and incremental exercise reduced, Na(+)-K(+)-ATPase activity. However, the small LHTL-induced depression of 3-O-MFPase activity was insufficient to adversely affect either K(+) regulation or total work performed.