Lower extremity muscle activity during deep-water running on self-determined pace

Although deep-water running (DWR) is often used to obtain the benefits of aerobic fitness and to reduce vertical component stress, its attendant muscle stress remains unclear. The present study investigated lower extremity muscle activity and during DWR compared to that during land walking (LW) and water walking (WW). Surface electromyography was used to evaluate muscle activity in nine healthy adults during each exercise at self-determined slow, moderate, and fast paces. The duration of swing phase, ankle, knee and hip joint angle, and each joint range of motion (ROM) also investigated. Results show that the percentages of maximal voluntary contraction (%MVC) of the soleus and medial gastrocnemius were lower during DWR than during LW or WW in the backward swing phase. The %MVC of the rectus femoris was higher during WW and DWR than during LW; that of the vastus lateralis was lower during WW and DWR than during LW in the forward swing phase. In the biceps femoris, the %MVC was higher during DWR than during LW or WW in the forward and backward swing phase. Every pace showed a similar trend. These results suggest that DWR can stimulate the hip joint flexor or extensor muscles.     

Mitochondrial creatine kinase activity alterations in skeletal muscle during long-distance running

In human gastrocnemius muscle obtained from long-distance runners, mitochondrial creatine kinase (CK) activities were significantly greater than nonrunning control skeletal muscle and significantly increased during training for and after a marathon race. Thus skeletal muscle tended to become similar to heart muscle in its mitochondrial CK composition. Total muscle CK activity was significantly different in males and females, was unaffected by marathon training and racing, and was similar to gastrocnemius muscle obtained from nonrunning controls. There was an inverse correlation between the maximum O2 uptake and the percentage increase in mitochondrial CK activity after training. These studies suggest that mitochondrial CK may play a key role in the intracellular transport of energy from mitochondrial to myofibrils in skeletal muscle during endurance exercise such as long-distance running.     

Differences in muscle function during walking and running at the same speed

Individual muscle contributions to body segment mechanical energetics and the functional tasks of body support and forward propulsion in walking and running at the same speed were quantified using forward dynamical simulations to elucidate differences in muscle function between the two different gait modes. Simulations that emulated experimentally measured kinesiological data of young adults walking and running at the preferred walk-to-run transition speed revealed that muscles use similar biomechanical mechanisms to provide support and forward propulsion during the two tasks. The primary exception was a decreased contribution of the soleus to forward propulsion in running, which was previously found to be significant in walking. In addition, the soleus distributed its mechanical power differently to individual body segments between the two gait modes from mid- to late stance. In walking, the soleus transferred mechanical energy from the leg to the trunk to provide support, but in running it delivered energy to both the leg and trunk. In running, earlier soleus excitation resulted in it working in synergy with the hip and knee extensors near mid-stance to provide the vertical acceleration for the subsequent flight phase in running. In addition, greater power output was produced by the soleus and hip and knee extensors in running. All other muscle groups distributed mechanical power among the body segments and provided support and forward propulsion in a qualitatively similar manner in both walking and running.     

Preferred step frequency during downhill running may be determined by muscle activity

It is well established that metabolic cost is minimized at an individual’s running preferred step frequency (PSF). It has been proposed that the metabolic minimum at PSF is due to a tradeoff between mechanical factors, however, this ignores muscle activity, the primary consumer of energy. Thus, we hypothesized that during downhill running, total muscle activity would be greater with deviations from PSF. Specifically, we predicted that slow step frequencies would have greater stance activity while fast step frequencies would have greater swing activity. We collected metabolic cost and leg muscle activity data while 10 healthy young adults ran at 3.0 m/s for 5 min at level and downhill at PSF and ±15% PSF. In support of our hypothesis, there was a significant main effect for step frequency for both metabolic cost and total muscle activity. In addition, there was greater muscle activity in the stance phase during the slower step frequency while muscle activity was greater in the swing phase during the fast step frequency. This suggests that PSF is partially determined by the tradeoff between the greater cost of muscle activity in the swing phase and lower cost in the stance phase with faster step frequency.     

Differences in muscle activity between natural forefoot and rearfoot strikers during running

Running research has focused on reducing injuries by changing running technique. One proposed method is to change from rearfoot striking (RFS) to forefoot striking (FFS) because FFS is thought to be a more natural running pattern that may reduce loading and injury risk. Muscle activity affects loading and influences running patterns; however, the differences in muscle activity between natural FFS runners and natural RFS runners are unknown. The purpose of this study was to measure muscle activity in natural FFS runners and natural RFS runners. We tested the hypotheses that tibialis anterior activity would be significantly lower while activity of the plantarflexors would be significantly greater in FFS runners, compared to RFS runners, during late swing phase and early stance phase. Gait kinematics, ground reaction forces and electromyographic patterns of ten muscles were collected from twelve natural RFS runners and ten natural FFS runners. The root mean square (RMS) of each muscle?s activity was calculated during terminal swing phase and early stance phase. We found significantly lower RMS activity in the tibialis anterior in FFS runners during terminal swing phase, compared to RFS runners. In contrast, the medial and lateral gastrocnemius showed significantly greater RMS activity in terminal swing phase in FFS runners. No significant differences were found during early stance phase for the tibialis anterior or the plantarflexors. Recognizing the differences in muscle activity between FFS and RFS runners is an important step toward understanding how foot strike patterns may contribute to different types of injury.     

Human muscle metabolism during sprint running

Biopsy samples were obtained from vastus lateralis of eight female subjects before and after a maximal 30-s sprint on a nonmotorized treadmill and were analyzed for glycogen, phosphagens, and glycolytic intermediates. Peak power output averaged 534.4 +/- 85.0 W and was decreased by 50 +/- 10% at the end of the sprint. Glycogen, phosphocreatine, and ATP were decreased by 25, 64, and 37%, respectively. The glycolytic intermediates above phosphofructokinase increased approximately 13-fold, whereas fructose 1,6-diphosphate and triose phosphates only increased 4- and 2-fold. Muscle pyruvate and lactate were increased 19 and 29 times. After 3 min recovery, blood pH was decreased by 0.24 units and plasma epinephrine and norepinephrine increased from 0.3 +/- 0.2 nmol/l and 2.7 +/- 0.8 nmol/l at rest to 1.3 +/- 0.8 nmol/l and 11.7 +/- 6.6 nmol/l. A significant correlation was found between the changes in plasma catecholamines and estimated ATP production from glycolysis (norepinephrine, glycolysis r = 0.78, P less than 0.05; epinephrine, glycolysis r = 0.75, P less than 0.05) and between postexercise capillary lactate and muscle lactate concentrations (r = 0.82, P less than 0.05). The study demonstrated that a significant reduction in ATP occurs during maximal dynamic exercise in humans. The marked metabolic changes caused by the treadmill sprint and its close simulation of free running makes it a valuable test for examining the factors that limit performance and the etiology of fatigue during brief maximal exercise.     

Leg kinematics and muscle activity during treadmill running in the cockroach, Blaberus discoidalis: II. Fast running

We have combined kinematic and electromyogram (EMG) analysis of running Blaberus discoidalis to examine how middle and hind leg kinematics vary with running speed and how the fast depressor coxa (Df) and fast extensor tibia (FETi) motor neurons affect kinematic parameters. In the range 2.5–10 Hz, B. discoidalis increases step frequency by altering the joint velocity and by reducing the time required for the transition from flexion to extension. For both Df and FETi the timing of recruitment coincides with the maximal frequency seen for the respective slow motor neurons. Df is first recruited at the beginning of coxa-femur (CF) extension. FETi is recruited in the latter half of femur-tibia (FT) extension during stance. Single muscle potentials produced by these fast motor neurons do not have pronounced effects on joint angular velocity during running. The transition from CF flexion to extension was abbreviated in those cycles with a Df potential occurring during the transition. One effect of Df activity during running may be to phase shift the beginning of joint extension so that the transition is sharpened. FETi is associated with greater FT extension at higher running speeds and may be necessary to overcome high joint torques at extended FT joint angles. Accepted: 24 May 1997     

EMG activity during positive-pressure treadmill running

Success has been demonstrated in rehabilitation from certain injuries while using positive-pressure treadmills. However, certain injuries progress even with the lighter vertical loads. Our purpose was to investigate changes in muscle activation for various lower limb muscles while running on a positive-pressure treadmill at different amounts of body weight support. We hypothesized that some muscles would show decreases in activation with greater body weight support while others would not.Eleven collegiate distance runners were recruited. EMG amplitude was measured over 12 lower limb muscles. After a short warm-up, subjects ran at 100%, 80%, 60%, and 40% of their body weight for two minutes each. EMG amplitudes were recorded during the final 30 s of each stage.Most muscles demonstrated lower amplitudes as body weight was supported. For the hip adductors during the swing phase and the hamstrings during stance, no significant trend appeared.Positive-pressure treadmills may be useful interventions for certain injuries. However, some injuries, such as hip adductor and hamstring tendonitis or strains may require alternative cross-training to relieve stress on those areas. Runners should be careful in determining how much body weight should be supported for various injuries to return to normal activity in the shortest possible time.     

The energetic cost of maintaining lateral balance during human running

To quantify the energetic cost of maintaining lateral balance during human running, we provided external lateral stabilization (LS) while running with and without arm swing and measured changes in energetic cost and step width variability (indicator of lateral balance). We hypothesized that external LS would reduce energetic cost and step width variability of running (3.0 m/s), both with and without arm swing. We further hypothesized that the reduction in energetic cost and step width variability would be greater when running without arm swing compared with running with arm swing. We controlled for step width by having subjects run along a single line (zero target step width), which eliminated any interaction effects of step width and arm swing. We implemented a repeated-measures ANOVA with two within-subjects fixed factors (external LS and arm swing) to evaluate main and interaction effects. When provided with external LS (main effect), subjects reduced net metabolic power by 2.0% (P = 0.032) and step width variability by 12.3% (P = 0.005). Eliminating arm swing (main effect) increased net metabolic power by 7.6% (P < 0.001) but did not change step width variability (P = 0.975). We did not detect a significant interaction effect between external LS and arm swing. Thus, when comparing conditions of running with or without arm swing, external LS resulted in a similar reduction in net metabolic power and step width variability. We infer that the 2% reduction in the net energetic cost of running with external LS reflects the energetic cost of maintaining lateral balance. Furthermore, while eliminating arm swing increased the energetic cost of running overall, arm swing does not appear to assist with lateral balance. Our data suggest that humans use step width adjustments as the primary mechanism to maintain lateral balance during running.     

Metabolic cost of generating horizontal forces during human running.

Previous studies have suggested that generating vertical force on the ground to support body weight (BWt) is the major determinant of the metabolic cost of running. Because horizontal forces exerted on the ground are often an order of magnitude smaller than vertical forces, some have reasoned that they have negligible cost. Using applied horizontal forces (AHF; negative is impeding, positive is aiding) equal to -6, -3, 0, +3, +6, +9, +12, and +15% of BWt, we estimated the cost of generating horizontal forces while subjects were running at 3.3 m/s. We measured rates of oxygen consumption (VO2) for eight subjects. We then used a force-measuring treadmill to measure ground reaction forces from another eight subjects. With an AHF of -6% BWt, VO2 increased 30% compared with normal running, presumably because of the extra work involved. With an AHF of +15% BWt, the subjects exerted approximately 70% less propulsive impulse and exhibited a 33% reduction in VO2. Our data suggest that generating horizontal propulsive forces constitutes more than one-third of the total metabolic cost of normal running.     

An activation-recruitment scheme for use in muscle modeling

The derivation of a new activation-recruitment scheme and the results of a study designed to test its validity are presented. The activation scheme utilizes input data of processed surface EMG signals, muscle composition, muscle architecture, and experimentally determined activation coefficients. In the derivation, the relationship between muscle activation and muscle fiber recruitment was considered. In the experimental study, triceps muscle force was determined for isometric elbow extension tasks varying in intensity from 10 to 100% of a maximum voluntary contraction (MVC) using both a muscle model that incorporates the activation scheme, and inverse dynamics techniques. The forces calculated using the two methods were compared statistically. The modeled triceps force was not significantly different from the experimental results determined using inverse dynamics techniques for average activation levels greater than 25% of MVC, but was significantly different for activation levels less than 25% of MVC. These results lend support for use of the activation-recruitment scheme for moderate to large activation levels, and suggest that factors in addition to fiber recruitment play a role in force regulation at lower activation levels.     

An improved glucoseoxidase--peroxidase-coupled assay for -fructofuranosidase activity

An improved glucoseoxidase-peroxidase-coupled assay for the determination of β-fructofuranosidase activity is described. The method makes use of the double effect of Tris (2-amino-2-hydroxymethylpropane-1,3-diol) as an inhibitor of both invertase and contaminating glucosidases. The method is very sensitive and is suitable for routine determinations. The total time needed for a single analysis is less than half an hour.     

Reproducibility of gastrocnemius medialis muscle architecture during treadmill running

The purpose of this study was to assess the reproducibility of fascicle length (FL) and pennation angle (PA) of gastrocnemius medialis (GM) muscle during running in vivo. Twelve male recreational long distance runners (mean ± SD; age: 24 ± 3 years, mass: 76 ± 7 kg) ran on a treadmill at a speed of 3.0 m/s, wearing their own running shoes, for two different 10 min sessions that were at least 2 days apart. For each test day 10 acceptable trials were recorded. Ankle and knee joint angle data were recorded by a Vicon 624 system with three cameras operating at 120 Hz. B-mode ultrasonography was used to examine fascicle length and pennation angle of gastrocnemius medialis muscle. The ultrasound probe was firmly secured on the muscle belly using a lightweight foam fixation. The results indicated that fascicle length and pennation angle demonstrated high reproducibility values during treadmill running both for within and between test days. The root mean square scores between the repeated waveforms of pennation angle and fascicle length were small (∼2° and ∼3.5 mm, respectively). However, ∼14 trials for pennation angle and ∼9 trials for fascicle length may be required in order to record accurate data from muscle architecture parameters. In conclusion, ultrasound measurements may be highly reproducible during dynamic movements such as treadmill running, provided that a proper fixation is used in order to assure the constant location and orientation of the ultrasound probe throughout the movement.     

A hypothesis for the function of braking forces during running turns

We examined the functional role of braking forces observed when humans execute turning maneuvers. Deceleration caused by braking forces contributes to changing the movement direction of the center of mass (COM) and maintaining constant velocity. We argue that braking forces also prevent over-rotation of the body about the vertical axis during maneuvers. We analyzed data from sidestep and crossover cuts at average initial running velocities of 3 m s(-1). Absent braking, lateral forces would result in body rotations 1.4-3 times the change in COM movement direction, causing the orientation of the body to be substantially mis-aligned with the direction of movement at the end of the step. A simple model based on the hypothesis that body rotation should match COM deflection can explain 70% of the variance in braking forces employed during running turns.     

Lower extremity muscle activation during horizontal and uphill running

Sloniger, Mark A., Kirk J. Cureton, Barry M. Prior, andEllen M. Evans. Lower extremity muscle activationduring horizontal and uphill running. J. Appl.Physiol. 83(6): 2073-2079, 1997.To provide more comprehensive information on theextent and pattern of muscle activation during running, we determinedlower extremity muscle activation by using exercise-induced contrastshifts in magnetic resonance (MR) images during horizontal and uphillhigh-intensity (115% of peak oxygen uptake) running to exhaustion(2.0-3.9 min) in 12 young women. The mean percentage of musclevolume activated in the right lower extremity was significantly(P <0.05) greater during uphill (73 ± 7%) than during horizontal (67 ± 8%) running. Thepercentage of 13 individual muscles or groups activated varied from 41 to 90% during horizontal running and from 44 to 83% during uphillrunning. During horizontal running, the muscles or groups mostactivated were the adductors (90 ± 5%), semitendinosus (86 ± 13%), gracilis (76 ± 20%), biceps femoris (76 ± 12%), andsemimembranosus (75 ± 12%). During uphill running, the musclesmost activated were the adductors (83 ± 8%), biceps femoris (79 ± 7%), gluteal group (79 ± 11%), gastrocnemius (76 ± 15%), and vastus group (75 ± 13%). Compared with horizontalrunning, uphill running required considerably greater activation of thevastus group (23%) and soleus (14%) and less activation of the rectusfemoris (29%), gracilis (18%), and semitendinosus (17%). We concludethat during high-intensity horizontal and uphill running to exhaustion,lasting 2-3 min, muscles of the lower extremity are not maximallyactivated, suggesting there is a limit to the extent to whichadditional muscle mass recruitment can be utilized to meet the demandfor force and energy. Greater total muscle activation during exhaustive uphill than during horizontal running is achieved through an altered pattern of muscle activation that involves increased use of some muscles and less use of others.

     

An improved viscosimetric assay for vertebrate collagenase activity

An improved viscosimetric assay for vertebrate collagenase acitivity is described. The assay is carried out at 35 degrees C in the presence of 1 M glucose to prevent fibril formation. The decrease in viscosity is linear with ime and proportional to enzyme concentration.