Plantar Flexor Muscle Group Research Articles

Nitric Oxide Synthase In Skeletal Muscle Repair Following Strain Injury

0057 Following muscle injury, satellite cells are recruited and activated to enable muscle repair. Previous studies using nitric oxide synathase (NOS) inhibition, mdx dystrophy mice and NOS-I knock-out mice have suggested that nitric oxide release may mediate satellite cell activation. PURPOSE: To assess the presence of NOS in strain-induced muscle injury in conjunction with two muscle regulatory factors: MyoD and myogenin. METHODS: Using female Sprague Dawley rats, muscle strains were produced by manually stretching (50 repetitions) an activated plantar flexor group through its normal range of motion. Muscle biopsy samples were evaluated 48- hours after strain injury for the presence of nitric oxide synthase, MyoD, and myogenin using Western immunoblot analysis. Transcript levels for neuronal (n) NOS, endothelial (e) NOS, inducible (i) NOS, MyoD and myogenin were assessed using reverse transcriptase polymerase chain reaction (RT-PCR) and kinetic PCR. RESULTS: An increase in myogenin transcripts and a decrease in nNOS transcript expression was observed 48- hours post-strain injury by RT-PCR. Western immunoblot analysis revealed increased eNOS, MyoD, and myogenin protein levels 48- hours post-strain injury, but a decrease in nNOS protein levels. CONCLUSION: NOS has been reported to play a role in muscle repair. Although nNOS expression was decreased, eNOS expression increased providing support for other NOS isoforms in muscle repair. Supported by NIOSH R01-OH-02918.

Physiological coxa varus?genu valgus influences internal knee and ankle joint moments in females during crossover cutting

This study evaluated the ankle and knee electromyographic, kinematic, and kinetic differences of 20 nonimpaired females with either neutral (group 1) or coxa varus-genu valgus (group 2) alignment during crossover cutting stance phase. Two-way mixed model ANOVA (group, session) assessed mean differences ( p<0.05) and correlation analysis further delineated relationships. During impact absorption, group 2 displayed earlier peak horizontal braking (anterior-posterior) ground reaction force timing, decreased and earlier peak internal knee extension moments (eccentric function), and earlier peak internal ankle dorsiflexion moment timing (eccentric function). During the pivot phase, group 2 displayed later and eccentrically-biased peak ankle plantar flexion moments, increased peak internal knee flexion moments (eccentric function), and later peak knee internal rotation timing. Correlation analysis revealed that during impact absorption, subjects with coxa varus-genu valgus alignment (group 2) displayed a stronger relationship between knee internal rotation velocity and peak internal ankle dorsiflexion moment onset timing ( r= -0.64 vs r = -0.26) and between peak horizontal braking ground reaction forces and peak internal ankle dorsiflexion moment onset timing ( r= 0.61 vs r= 0.24). During the pivot phase these subjects displayed a stronger relationship between peak horizontal braking ground reaction forces and peak internal ankle plantar flexion moment onset timing ( r= -0.63 vs r= -0.09) and between peak horizontal braking forces and peak internal ankle plantar flexion moments ( r= -0.72 vs r= -0.26). Group differences suggest that subjects with coxa varus-genu valgus frontal-plane alignment have an increased dependence on both ankle dorsiflexor and plantar flexor muscle group function during crossover cutting. Greater dependence on ankle muscle group function during the performance of a task that requires considerable 3D dynamic knee joint control suggests a greater need for frontal and transverse plane weight bearing tasks that facilitate eccentric ankle muscle group function to optimize injury prevention conditioning and post-surgical rehabilitation programs.

EFFECTS OF LONG-TERM RESISTIVE TRAINING ON BODY COMPOSITION IN OLDER DIABETIC AND WELL ADULTS

Body composition changes, especially sarcopenia, are factors that may influence physical capabilities and functional independence in older adults. The impact of long-term strength training and whether or not the influence is similar for older adults with diabetes and well older adults is unclear. PURPOSE This study was designed to evaluate the effects of a 24-month resistive training intervention on body composition, including sarcopenia in older diabetic and well adults. METHODS A total of 107 older adults (52 with diabetes, age 66.1 yr; 29 exercisers (DE) and 23 comparisons - DC) (55 well, age 71.6 yr; 30 exercisers (WE) and 25 comparisons - WC) served as subjects. The DE and WE resistive trained 3 times a week, an hour a day. The subjects trained at 50%, 60% and 70% of their one repetition maximum (1RM) and the training sessions consisted of 10 minutes of warm-up and flexibility exercises, and 50 minutes of resistive training. The subjects trained 5 upper extremity (biceps, triceps, arm cross, pullover and lateral raises), 3 trunk (abdomen, low back and torso arm) and 3 lower extremity (knee extensors, knee flexors and plantar flexor) muscle groups on a multi-station Nautilus system. They were tested for 1RM at baseline, 12 and 24 months. The data were evaluated for differences with an ANOVA. RESULTS There was an increase (p <0.05) in strength for each of the 11 muscle groups for both the DE and WE at 12 and 24 months. The WE experienced a decrease in waist-hip ratio (p < 0.05) at 24 months. The DE experienced a decrease in thigh skinfolds (S) and thigh S/Circumference ratio at 24 months. There were no body composition changes for the WC and DC subjects. CONCLUSION These results suggest that older DE experience an increase and older WE no changes in thigh muscle mass following 24-month of training that include lower extremities. The different responses may be partially due to differences in sarcopenic state and metabolic responses during training. Supported by VA Medical Center contract number E721–4RA

Frontal plane knee angle affects dynamic postural control strategy during unilateral stance.

Center of plantar pressure (COPP) location moves toward the forefoot as ankle plantar flexor muscles attempt to maintain postural control during single leg stance. This study evaluated relationships between frontal plane tibiofemoral joint angulation during relaxed bilateral stance and mean COPP locations during vision-denied single leg stance at 20 degrees knee flexion. Fifty-six nonimpaired athletes (29 female, 27 male) were evaluated for frontal plane tibiofemoral joint angulation and standing foot angle by using two-dimensional videography (30 Hz). Mean anterior-posterior and mediolateral COPP locations were assessed during single leg stance on a mat (25 Hz, 15 s). One-way ANOVA and Tukey HSD tests evaluated group differences (P < or = 0.05) based on frontal plane tibiofemoral joint angulation. Group 1 (genu varus or genu valgus < 5 degrees ) displayed a mean anterior-posterior COPP location of 54.2 +/- 6% from the (0,0) coordinate starting point at the anterolateral foot (10.3 +/- 2 cm from the posterior sensor edge). Group 2 (genu varus angulation > or = 5 degrees ) and group 3 subjects (genu valgus angulation > or = 5 degrees ) displayed mean anterior-posterior COPP locations of 60.6 +/- 8% and 60.7 +/- 7% (8.8 +/- 2 cm and 8.7 +/- 2 cm from the posterior sensor edges), respectively. Group 2 (12.5 +/- 3 N x kg(-1)) and group 3 (12.4 +/- 3.1 N x kg(-1)) subjects also displayed greater mean plantar force magnitude/body weight than group 1 (10.3 +/- 2 N x kg(-1)) subjects. Mean ankle plantar flexor moment magnitudes did not differ between groups. Rearfoot directed mean anterior-posterior COPP locations and greater plantar force magnitudes/body weight suggests that subjects with genu varus or genu valgus relied more on the subtalar and midtarsal joint control function of the ankle plantar flexor muscle group for lower extremity dynamic postural control.

EFFECTS OF LONG-TERM RESISTIVE TRAINING ON STRENGTH IN OLDER DIABETIC AND WELL ADULTS

Older diabetic adult (especially type2) have a greater body weight (subcutaneous fat deposits), reduced muscular insulin sensitivity, altered thermogenesis, and decreased peripheral neurological, muscular and circulatory functions. Whether or not their strength responses to training will be similar to well older adults is unclear. PURPOSE: Therefore, this study was designed to evaluate the effects of a 24-month resistive training intervention on total body strength responses in older diabetic and well adults. METHODS: A total of 107 older adults (52 diabetics, age 66.1 yr û 29 exercisers (DE) and 23 comparisons (DC) and 55 well, age 71.6 yr û 30 exercisers (WE) and 25 comparisons WC) served as subjects. The DE and WE resistive trained 3 times a week, an hour a day for the first 6 months and 2 days a week the last 18 months. The subjects trained at 50%, 60% and 70% of their one repetition maximum (1RM) and the training sessions consisted of 10 minutes of warn-up and flexibility exercises, and 50 minutes of resistive training. The subjects trained 5 upper extremity (biceps, triceps, arm cross, pullover and lateral raises), 3 trunk (abdomen, low back and torso arm) and 3 lower extremity (knee extensors, knee flexors and plantar flexor) muscle groups on a multi-station Nautilus system. They were tested for strength at baseline and at 6-month intervals. The data were evaluated for differences with an ANOVA. RESULTS: There was an increase (p < 0.05) in strength for each of the 11 muscle groups for both the DE and WE at 6 months. Gains significantly above baseline that ranged from 24.7% to 37% for total body strength were maintained for the duration of the 24-month intervention for both the DE and WE. There were no strength gains for the DC or WC subjects. The pattern of strength gains were similar for the DE and WE at 6 and 12 months, but gains for the DE at 18 and 24 months were less than for the WE. CONCLUSIONS: These results suggests that older diabetics receive similar strength gains from resistive training as well older adults up to 12 months, but from 12 to 24 months older diabetics are less able to retain the gains obtained earlier even though they continue training. Supported by VA Medical Center contract number E721-4RA

Contributions of the individual ankle plantar flexors to support, forward progression and swing initiation during walking

Walking is a motor task requiring coordination of many muscles. Previous biomechanical studies, based primarily on analyses of the net ankle moment during stance, have concluded different functional roles for the plantar flexors. We hypothesize that some of the disparities in interpretation arise because of the effects of the uniarticular and biarticular muscles that comprise the plantar flexor group have not been separated. Furthermore, we believe that an accurate determination of muscle function requires quantification of the contributions of individual plantar flexor muscles to the energetics of individual body segments. In this study, we examined the individual contributions of the ankle plantar flexors (gastrocnemius (GAS); soleus (SOL)) to the body segment energetics using a musculoskeletal model and optimization framework to generate a forward dynamics simulation of normal walking at 1.5 m/s. At any instant in the gait cycle, the contribution of a muscle to support and forward progression was defined by its contribution to trunk vertical and horizontal acceleration, respectively, and its contribution to swing initiation by the mechanical energy it delivers to the leg in pre-swing (i.e., double-leg stance prior to toe-off). GAS and SOL were both found to provide trunk support during single-leg stance and pre-swing. In early single-leg stance, undergoing eccentric and isometric activity, they accelerate the trunk vertically but decelerate forward trunk progression. In mid single-leg stance, while isometric, GAS delivers energy to the leg while SOL decelerates it, and SOL delivers energy to the trunk while GAS decelerates it. In late single-leg stance through pre-swing, though GAS and SOL both undergo concentric activity and accelerate the trunk forward while decelerating the downward motion of the trunk (i.e., providing forward progression and support), they execute different energetic functions. The energy produced from SOL accelerates the trunk forward, whereas GAS delivers almost all its energy to accelerate the leg to initiate swing. Although GAS and SOL maintain or accelerate forward motion in mid single-leg stance through pre-swing, other muscles acting at the beginning of stance contribute comparably to forward progression. In summary, throughout single-leg stance both SOL and GAS provide vertical support, in mid single-leg stance SOL and GAS have opposite energetic effects on the leg and trunk to ensure support and forward progression of both the leg and trunk, and in pre-swing only GAS contributes to swing initiation.

Inactivity and muscle: effect of resistance training during bed rest on muscle size in the lower limb.

The present study aimed to investigate the effect of dynamic leg press training on the physiological cross-sectional areas (PCSAs) of human lower limb muscles during 20 days of 6 degrees head-down tilt bed rest. Five healthy men comprised the resistance training group (BR-Tr) and data from two previous studies were used to derive a 10-man control group (BR-Cont). The BR-Tr performed two sessions (morning and afternoon session) of dynamic leg press action including knee extension and plantar flexion daily for the bed rest period: (1) three sets of 10 repetitions at 90% of maximum load and (2) 40% of maximum load to exhaustion. The PCSAs of the knee extensor (KE), knee flexor (KF), plantar flexor (PF), and dorsiflexor muscle groups were estimated using serial axial magnetic resonance (MR) images of the right-thigh and leg. After the bed rest period, the BR-Tr showed a significant increase in the PCSA of the KE. Although PCSA of the KF in two groups significantly decreased after bed rest, percentage of change in PCSA of the biceps femoris (long head) and semitendinosus muscles in the BR-Tr, which occupied approximately 70% of the KF, was significantly higher than those in the BR-Cont. Both the BR-Tr and BR-Cont groups showed significant decreases in the PCSA of PF with similar magnitude of 11.6% (P < 0.001) and 11.9% (P < 0.001), respectively. These results suggest that dynamic leg press training during bed rest can prevent deteriorating of the KE and a part of KF, but not the calf muscles.

Effect of short-duration spaceflight on thigh and leg muscle volume.

Human skeletal muscle probably atrophies as a result of spaceflight, but few studies have examined this issue. Thus, little is known about the influence of microgravity upon human skeletal muscle, nor is it possible to assess the validity of ground based models of spaceflight. This study tested the hypothesis that the magnitude of spaceflight induced muscle atrophy would be a function of flight duration and greater than that of bed rest. Three astronauts flew 9, 15, and 16 d in space. Volume of the knee extensor (quadriceps femoris), knee flexor (hamstrings, sartorius, and gracilis), and plantar flexor (triceps surae) muscle groups was measured using magnetic resonance imaging before and after spaceflight and during recovery. The volume of each muscle group in each image was determined by multiplying cross-sectional area by slice thickness. These values were subsequently summed to calculate muscle volume. Volume changes in the knee extensor, knee flexor, and plantar flexor muscle groups ranged from -15.4 to -5.5, -14.1 to -5.6, and -8.8 to -15.9%, respectively. Muscle volume decreases normalized by flight duration ranged from 0.62 to 1.04% x d(-1). These relative changes appeared to be greater than those that we have reported previously for bed rest (Akima et al., J. Gravitat. Physiol. 4:15-22, 1997). These results suggest that atrophy as a result of at least 2 wk of spaceflight varied among individuals and muscle groups and that the degree of atrophy appeared to be greater than that induced by 20 d of bed rest.

POST ACTIVATION POTENTIATION IN HUMAN DORSIFLEXOR AND PLANTARFLEXOR MUSCLES FOLLOWING ISOMETRIC, ECCENTRIC AND CONCENTRIC CONTRACTIONS

1042 The effect of contraction type on post activation potentiation (PAP) in the dorsiflexor (DF) and plantarflexor (PF) muscles was determined following maximal voluntary contractions (MVC) in 10 men (mean age = 25.2 yr). Subjects were tested on three separate days in which they performed one maximal dorsiflexion and one maximal plantarflexion contraction, in either an isometric (ISO), eccentric (ECC), or concentric (CON) mode. ISO MVC's were maintained for 5s, and ECC and CON MVC's were measured at 10 degrees/s, such that the total contraction time was also 5s. Maximal twitches were evoked immediately following the MVC and at 30s intervals thereafter, for a total of 5 min. The muscle compound action potential (M-wave) was also recorded. A significant increase in peak twitch was demonstrated immediately following all 3 contraction types in both the DF and PF muscle groups (PAP of 74% in DF, 23% in PF). No significant differences were observed between contraction types in PAP. The potentiated twitch was associated with a significantly faster rise time (TPT) and half-relaxation time (1/2RT) in PF (TPT: 103msec vs. 91msec; 1/2RT: 52msec vs. 46msec, in baseline vs. potentiated conditions, respectively), but not in DF. The M-wave area was significantly potentiated after the DF MVC's (peak increase of 13%), and was significantly greater in CON vs. ECC contractions. There was no significant change in M-wave area in the PF contractions. These results suggest that there is no effect of contraction type on the magnitude of PAP in the DF or PF muscles, however PAP is greater in DF vs. PF. There appears to be a corresponding increase in M-wave area following DF MVC's, however this potentiation is longer lasting and reaches its peak after the point where peak PAP is achieved.

Reliability of Measuring Voluntary Strength and Isometric Twitch Properties in the Ankle Muscles of Very Old Adults

The purpose of this study was to assess the reliability of measuring voluntary isometric strength, evoked isometric twitch properties (peak torque, time to peak torque, half-relaxation time), M-wave amplitude, and passive tension in very old adults (73-92 years). Five male and 5 female subjects were tested on two different test occasions that were 1 week apart. Using the intraclass correlation coefficient (ICC) method, the mean reliability coefficient of all measurements on the dorsiflexor (DF) and plantar flexor (PF) muscle groups was .91 ± .05. Similar ICC values were found for DF and PF muscles (.92 ± .04 and .90 ± .05, respectively). Resting PF half-relaxation time was the least reliable measure, with an ICC value of .80, while maximum voluntary strength was the most reliable with ICC values of .98 for DF and .97 for PF. The variation ranged from 0.2 to 12.3%. It was concluded that ankle muscle function (both voluntary and evoked) can be reliably assessed in this very old age group.

Recovery of muscle transfers replacing the total plantar flexor muscle group in rats.

In rats, combinations of plantar flexor muscles representing approximately 20, 40, 60, and 80% of the mass of the total plantar flexor group were transferred orthotopically in the absence of synergistic muscles and allowed to recover for 120 days. We hypothesized that, compared with their individual control values for structural and functional variables, the transfers would display a hierarchical array of deficits, proportional to their initial mass and, consequently, inversely proportional to the relative load on the transfers. Surprisingly, compared with their individual control values, each muscle transfer displayed deficits of 30-40% in muscle mass, total fiber cross-sectional area, and maximum isometric force, with the exception of the smallest transfer, the plantaris (PLN) muscle, which recovered 100% of its control value for each of these variables. Therefore, except for the PLN transfer, the muscle transfers studied displayed deficits similar in magnitude to those reported for muscles transferred in the presence of synergistic muscles. The greater recovery of the PLN transfer was attributed to the relatively large requirement for force production imposed on this transfer due to the average force requirements of the total plantar flexor group.

Functional Evaluation at the Medial Gastrocnemius Donor Site in Rats

The transfer of a skeletal muscle from a donor to a recipient site creates an initial deficit in the structure and function of the muscle group from which it originates. Removal of the donor muscle induces hypertrophy of the remaining synergistic muscles, which compensate for part of the deficit at the donor site. The medial gastrocnemius (MGN) muscle is a frequently utilized donor muscle. Compared with the mass and force production of the control four-muscle plantar flexor group in rats, removal of the MGN muscle creates an initial deficit of approximately 36 percent. At 60, 90, and 120 days after removal of the MGN muscle, the degree of compensation of the remaining three-muscle plantar flexor group (lateral gastrocnemius, soleus, and plantaris muscles) was evaluated. The mass of the three-muscle group increased 13 percent over the time course studied, but was still 28 percent less than the mass of the control four-muscle group. Similarly, the maximum force of the three-muscle group increased 27 percent, but was 21 percent lower than the control four-muscle group. The authors propose a model that illustrates the function restored at a donor site in terms of the percentage of the total muscle group comprised by the donor muscle and the ability of the remaining muscle group to compensate for its removal.

Recovery of medial gastrocnemius muscle grafts in rats: implications for the plantar flexor group

Medial gastrocnemius (MGN) muscles were grafted in 18 rats and evaluated at 60, 90, and 120 days after the operation. Our purpose was to investigate the degree of recovery of the vascularized MGN grafts and the entire plantar flexor muscle group. Compared with control values, muscle mass and maximum force of MGN grafts were decreased by 33 and 38% at 60 days, 22 and 32% at 90 days, and 13 and 15% at 120 days. At 60 and 90 days, the deficits in maximum force for the entire plantar flexor muscle group, including the graft, were 29 and 17%, respectively. No difference was observed at 120 days. At 60 days, the deficit in the total mass of the plantar flexor group was 14% compared with control values, but by 90 days no deficit was observed. The restoration of normal plantar flexor group structure and function indicates that the degree of recovery attained by MGN grafts, although not complete, was sufficient to ensure that the performance of the total muscle group was not compromised.

Effects of Cold Water Application on Isokinetic Strength of the Plantar Flexors

Cold (cryotherapy) is commonly applied to an athlete immediately before and/or after sports participation. The purpose of this study was to determine the effect of cold water submersion (CWS) on isokinetic strength of the plantar flexor muscle group. Eleven women and five men (mean age 22.1 years, height 170.8 cm, weight 64.5 kg) with no history of ankle joint pathology were tested for peak torque, average power, and total work of the dominant foot at 60 deg/sec with a Cybex II isokinetic dynamometer. Before isokinetic testing subjects were randomly assigned to either CWS or an inactive rest period (RP). Subjects returned 1 week later to receive the opposite treatment and undergo isokinetic testing. The CWS consisted of placing the leg in a 15°C tub of water for 20 minutes. The RP consisted of remaining seated for a 20-minute period. Paired t tests were computed to determine if any differences existed in peak torque, average power, and total work between the CWS and RP conditions. Results indicated concentric isokinetic strength values were lower after CWS for peak torque, average power and total work of the plantar flexor muscle group. These findings indicate that concentric isokinetic torque, power, and work of the plantar flexor muscle group are reduced immediately after CWS. Further research should be undertaken to determine the length of time isokinetic output is reduced before returning to normal responses after CWS is present.

An apparatus to measure in vivo biomechanical behavior of dorsi- and plantarflexors of mouse ankle.

We developed an apparatus to quantify the biomechanical behavior of the dorsi- and plantarflexor muscles of the ankle of an anesthetized mouse. When the dorsi- or plantarflexor muscle group is activated by electrical stimulation of either the peroneal or tibial nerve, the apparatus measures the moment developed about the ankle during isometric, isovelocity shortening, or isovelocity lengthening contractions. Displacements may be performed over the full 105 degrees range of ankle motion with an angular resolution of 0.09 degrees. Bidirectional isovelocity ramps in ankle angle up to 1,100 degrees/s are possible and are equivalent to maximum velocities of 2.3 fiber lengths/s (Lf/s) for the fibers in tibialis anterior muscle and 11.9 Lf/s for those in gastrocnemius muscle. During single contractions of the dorsi- and plantarflexor muscle groups at 37 degrees C and with both knee and ankle joint at 90 degrees neutral position, the isometric tetanic force developed was 1.4 and 3.3 N, power output at 2.2 Lf/s was 3.1 and 5.9 mW, and power absorption at 0.5 Lf/s was 4.9 and 9.0 mW, respectively. These values are in reasonable agreement with data from the same muscle groups tested in situ. We conclude that the apparatus provides valid measurements of force and power of the dorsi- and plantarflexor muscle groups.

A COMPARISON OF CONTRACTILE PROPERTIES IN THE PREFERRED AND NONPREFERRED LEG IN A MIXED SAMPLE OF DYSTROPHIC PATIENTS

No study of how muscle contractile function is related to limb preference in human muscular dystrophy is presently available. The purpose of this study was to determine if the ankle plantarflexor (PF) and dorsiflexor (DF) muscle groups of the preferred leg are more or less affected than the nonpreferred one in a mixed sample of myotonic and limb-girdle patients. Measurements of lower limb preference were made as well as of PF and DF evoked and voluntary contractile responses. Isometric contractile properties and peak values for torque production during maximum isometric twitch and voluntary contractions were measured. No significant difference was found in terms of contractile properties between the preferred and nonpreferred leg for both DF and PF muscle groups, except for the large PF twitch torque observed in the nonpreferred side (P less than 0.05). These results, however, reveal a clear tendency for both muscle groups on the preferred side to be weaker than those on the nonpreferred side. This last finding, in conjunction with the equally if not presumably stronger PF/DF muscles on the preferred leg of healthy adult subjects, would suggest that the equivalent bilateral muscle force observed in the present study may be interpreted as giving support to the hypothesis that overwork or overuse of dystrophic muscles may be harmful in weakening the musculature.

Strength of lower limb related to gait velocity and cadence in stroke patients

This study was undertaken to determine the relationship between two temporal components of gait (velocity and cadence) and the standardized static strength of seven lower extremity muscle groups of the paretic side of 20 patients who were hemiplegic following cerebrovascular accidents. Velocity and cadence were calculated from a timed gait trial over an eight-metre expanse of floor. Static strength was tested by a hand-held dynamometer, and the scores standardized against body weight. The muscles tested were hip flexors, extensors and abductors; the knee flexors and extensors; and the ankle dorsiflexors and plantar flexors. Correlations were significant (p &lt; 0.05) between both gait variables and the standardized strength of the hip extensor, knee flexor, ankle dorsiflexor, and ankle plantar flexor muscle groups. Also significant were the correlations between cadence and the standardized strength of the hip abductor and knee extensor muscles. These relationships suggest that the strength of some muscle groups of the paretic lower extremity may be of functional importance and worthy of measurement.

Plantar flexor strength testing using the cybex isokinetic dynamometer.

Twenty male subjects and twenty female subjects in each of three age categories, 6 to 8 years, 14 to 16 years, and 23 to 28 years, were tested on the Cybex Isokinetic Dynamometer to obtain normative strength values for the ankle plantar flexor muscle group. Values were established for both isokinetic and isometric contractions at two speeds. The results indicate that age and weight are the significant variables in determining strength scores.

Rat locomotory muscle fiber activity during trotting and galloping.

This study was designed to investigate the hypothesis that the trot-gallop transition in running guadrupeds occurs when active cross-sectional areas of muscles or fiber populations within muscles, reach some critical point as animals increase speed within trotting. Rats (Rattus norvegicus) were used as experimental animals, and glycogen depletion was used to estimate patterns or fiber activity. Our results indicate that 1) the contribution to power output by the front limb muscles was less than that of the hind limb muscles during trotting and galloping; 2) the active cross-sectional area of plantaris muscles peaked immediately prior to the transition in gait; 3) the ankle plantar flexor group of muscles as a whole did not attain a maximum active cross-sectional area during fast trotting; and 4) no major discontinuities in whole muscle or fiber type glycogen depletion rates occurred across the gait change. Although these findings do not prove the hypothesis, they support the concept that the trop-gallop transition follows the attainment of peak active muscle cross-sectional areas as animals increase trotting speed.