Comparing human skeletal muscle architectural parameters of cadavers with in vivo ultrasonographic measurements.

The purpose of this study was to document and compare the architectural parameters (fibre bundle length, angle of pennation) of human skeletal muscle in cadaveric specimens and live subjects. The medial (MG) and lateral (LG) gastrocnemius, and posterior (PS) and anterior (AS) soleus were examined bilaterally in 5 cadavers (mean age 72.6, range 65-83 y) and 9 live subjects (mean age 76.3, range 70-92 y). Data were obtained from direct measurement of cadaveric specimens and from ultrasonographic scans of the live subjects. In cadaveric muscle, fibre bundles were isolated; their length was measured in millimetres and pennation angles were recorded in degrees. In live muscle, similar measurements were taken from ultrasonographic scans of relaxed and contracted muscle. For the scans of relaxed muscle, subjects were positioned prone with the foot at a 90 degrees angle to the leg, and for scans of contracted muscle, subjects were asked to sustain full plantarflexion during the scanning process. Fibre bundle length and angle of pennation were compared at matched locations in both groups. It was found that the relationship between cadaveric and in vivo values for fibre length and angle of pennation varied between muscle parts. The cadaveric architectural parameters did not tend to lie consistently towards either extreme of relaxation or contraction. Rather, within MG, PS and AS, cadaveric fibre bundle lengths lay between those for relaxed and contracted in vivo muscle. Similarly both the anterior and posterior cadaveric fibre angles of pennation lay between the in vivo values within LG and PS. In summary, architectural characteristics of cadaveric muscle differ from both relaxed and contracted in vivo muscle. Therefore, when developing models of skeletal muscle based on cadaveric studies, the architectural differences between live and cadaveric tissue should be taken into consideration.

Exercise-enhanced satellite cell proliferation and new myonuclear accretion in rat skeletal muscle.

The effects of increased functional loading on early cellular regenerative events after exercise-induced injury in adult skeletal muscle were examined with the use of in vivo labeling of replicating myofiber nuclei and immunocyto- and histochemical techniques. Satellite cell proliferation in the soleus (Sol) of nonexercised rats (0.4 +/- 0.2% of fibers) was unchanged after an initial bout of declined treadmill exercise but was elevated after two (1.0 +/- 0.2%, P < or = 0.01), but not four or seven, daily bouts of the same task. Myonuclei produced over the 7-day period comprised 0.9-1.9% of myonuclei in isolated fibers of Sol, tibialis anterior, and vastus intermedius of nonexercised rats. The accretion of new myonuclei was enhanced (P < or = 0.05) in Sol and vastus intermedius by the initial exercise followed by normal activity (to 3.1-3.4% of myonuclei) and more so by continued daily exercise (4.2-5.3%). Observed coincident with a lower incidence of histological fiber injury and unchanged fiber diameter and myonuclei per millimeter, the greater new myonuclear accretion induced by continued muscle loading may contribute to an enhanced fiber repair and regeneration after exercise-induced injury.

Sonographic studies of human soleus and gastrocnemius muscle architecture: gender variability.

The purpose of this study was to establish if there are gender differences in muscle architecture in relaxed human soleus and gastrocnemius muscles of normal, live subjects. Ultrasonography was used to measure fiber bundle length, muscle thickness, and angles of pennation in a total of ten predetermined sites in the medial and lateral heads of gastrocnemius and the anterior and posterior soleus in 19 males and 16 females. Percentage differences between males and females for each parameter were recorded. Gender differences were statistically analyzed using multivariate analysis of variance. In the gastrocnemius and soleus muscles of males and females the differences between the overall fiber bundle length, angle of pennation and muscle thickness were statistically significant (P < 0.05). Overall, females were found to have longer average muscle fiber bundle length and males thicker muscles and larger angles of pennation. The greatest percentage differences of the architectural parameters between males and females were in the posterior soleus: 13% difference in fiber length and 26% difference in angle of pennation in the midline of posterior soleus and 26% difference in muscle thickness of the lateral part of posterior soleus. No correlation was found between leg length and fiber length, angle of pennation or muscle thickness. Fiber length (decreased), angle of pennation (greater) and muscle thickness (greater) of most parts of the gastrocnemius and soleus muscles were significantly different in males and females. Leg length of males and females did not correlate to these architectural parameters.

Expression of developmental myosin and morphological characteristics in adult rat skeletal muscle following exercise-induced injury.

The extent and stability of the expression of developmental isoforms of myosin heavy chain (MHCd), and their association with cellular morphology, were determined in adult rat skeletal muscle fibres following injury induced by eccentrically-biased exercise. Adult female Wistar rats [274 (10) g] were either assigned as non-exercised controls or subjected to 30 min of treadmill exercise (grade, -16 degrees; speed, 15 m x min(-1)), and then sacrificed following 1, 2, 4, 7, or 12 days of recovery (n = 5-6 per group). Histologically and immunohistologically stained serial, transverse cryosections of the soleus (S), vastus intermedius (VI), and tibialis anterior (TA) muscles were examined using light microscopy and digital imaging. Fibres staining positively for MHCd (MHCd+) were seldom detected in the TA. In the VI and S, higher proportions of MHCd+ fibres (0.8% and 2.5%, respectively) were observed in rats at 4 and 7 days post-exercise, in comparison to all other groups combined (0.2%, 1.2%; P < or = 0.01). In S, MHCd+ fibres were observed less frequently by 12 days (0.7%) than at 7 days (2.6%) following exercise. The majority (85.1%) of the MHCd+ fibres had morphological characteristics indicative of either damage, degeneration, repair or regeneration. Most of the MHCd+ fibres also expressed adult slow, and/or fast myosin heavy chain. Quantitatively, the MHCd+ fibres were smaller (< 2500 microm2) and more angular than fibres not expressing MHCd. Thus, there was a transient increase in a small, but distinct population of MHCd+ fibres following unaccustomed, functional exercise in adult rat S and VI muscles. The observed close coupling of MHCd expression with morphological changes within muscle fibres suggests that these characteristics have a common, initial exercise-induced injury-related stimulus.

The effect of bipolar electrocautery on peripheral nerves.

Although bipolar cautery was designed to minimize trauma to the central nervous system, little is known about the effects of bipolar cautery on peripheral nerve tissue. This experiment was designed to study the effect of direct bipolar cautery on a peripheral nerve and the muscles innervated by that nerve. Lewis rats (n = 200) were assigned to five different groups: control, sham, and three cautery groups (duration of either 0.5, 1.0, or 1.5 seconds). The hind limb tibial nerves were isolated in the sham group and isolated and cauterized in the cautery groups. Assessments performed at 2 hours, 2 weeks, 4 weeks, and 8 weeks postoperatively included isometric contractile function studies of both a fast- and a slow-twitch muscle, muscle weights, and nerve histology/morphometry. Significant muscle weight loss and reduced muscle function were found in the cautery groups at 2, 4, and 8 weeks (p < 0.05). Histologically, the nerves of the cautery groups showed nerve damage consistent with Sunderland's type 4 nerve injury when examined at 2 weeks and showed nerve regeneration at 4 and 8 weeks. Both the fast-twitch muscle and the shorter duration cautery were associated with faster recovery relative to the slow-twitch muscles and longer duration cautery, respectively. Bipolar cautery, as administered to rat tibial nerves in this experiment, is associated with a significant injury to the nerve and loss of function of the muscles innervated by the nerve.

Resolving discrepancies in image research: the importance of direct observation in the illustration of the human soleus muscle.

A historical analysis of fourteen published illustrations of the soleus muscle from the sixteenth to the twentieth century reveals obvious inconsistencies in the representational accuracy of the architecture of the muscle. To ensure the most accurate illustrations possible, biomedical communicators should conduct direct laboratory observations. A review of reference images alone is insufficient for assuring anatomical accuracy. Having followed this protocol, three architecturally distinct regions of soleus were observed and illustrated and the final results suggest that soleus is a complex multipennate muscle with significant architectural characteristics not typically represented in published illustrations.

Survey of factors influencing the selection of academic plastic surgeons.

The purpose of this study was to evaluate the importance of factors influencing the selection of candidates for academic positions in plastic surgery. This study reports the results of a survey investigating these factors. The survey was conducted in 1994, canvassing the chairpersons from the 120 plastic surgery programs in the United States and Canada with responses from 91 (76 percent) of the plastic surgery programs. The study examined individual accomplishments and areas of additional training. Training in a specific area of clinical interest, clinical and basic science experience, and training in cosmetic surgery were the most highly rated areas of additional training. The ideal time to receive this training was also assessed for each area of additional training. Postgraduate degrees in basic science, epidemiology, or clinical research were not highly rated. The highest rated personal accomplishments were the personal interview, letter of reference from the program chairperson, publications, and presentations. Despite the survey's attempt to evaluate factors other than personal characteristics (i.e., honesty, integrity, affability, etc.) more than 25 percent of the respondents indicated that these attributes are highly rated and cannot be judged separately. The information collected in this survey represents an opinion from 1994, which defines some of the factors that are considered important when residents and newly trained plastic surgeons are considering a career in academic plastic surgery.

Evidence for the migration of rat aortic endothelial cells toward the heart.

Most vascular endothelial cells at the edge of experimentally induced wounds have their centrosomes oriented toward the wound in the direction of cell migration. The finding that the centrosomes in endothelial cells of non-wounded aorta and vena cava are also oriented toward the heart suggested the hypothesis that endothelial cells are normally migrating in this direction. To test this hypothesis, endothelial cells in a segment of the rat abdominal aorta were labeled with a relatively nontoxic dye, 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI), and the position of the labeled cells was determined 3 and 6 weeks later. The results obtained showed that in 6 of the 9 rat aortas examined at 3 weeks and 15 of the 20 rat aortas examined at 6 weeks, DiI-labeled endothelial cells had migrated various distances up to 5000 microns toward the heart. In contrast, no migration of endothelial cells was detected at the opposite end of the labeled segment, in the direction away from the heart. These results demonstrate that vascular endothelial cells in the abdominal aorta of the rat are not stationary but are migrating toward the heart. The significance of the migration of endothelial cells toward the heart is presently unknown; however, it would be interesting to explore whether or not the impairment of this migration may contribute to disease processes in which the ability to maintain an intact and normally functioning endothelial cell lining is compromised as in atherosclerosis.

Differences between contractions of fast and slow muscles after nerve grafting.

The nature of reinnervation of fast- and slow-twitch skeletal muscles, as assessed by contractile characteristics, was determined in a rat sciatic-nerve graft model. The isometric contractile function of the fast-twitch plantaris and slow-twitch soleus muscles from hindlimbs of adult male Lewis rats (225 to 250 g) was assessed at 16 weeks after sciatic-nerve grafting. A 3-cm interposition sciatic-nerve graft was performed in the following groups: fresh syngeneic (n = 10), fresh allogeneic (n = 11), 3-week stored allogeneic (n = 9), and freeze-thawed allogeneic (n = 9). A control group consisted of 8 normal unoperated rats. Contractile properties were assessed by stimulating the muscles indirectly via the sciatic nerve. At 16 weeks, soleus and plantaris muscle masses were 40 and 52 percent of controls, while their respective absolute tetanic forces (N) were less than 65 and 45 percent of controls. Analysis of time-dependent contractile parameters showed that the soleus/plantaris ratios for time to peak tension (TTP) and maximum rate of force development (df/dt) were not significantly altered following grafting. However, the ratio for half relaxation time (1/2RT) was significantly reduced from 4.44 +/- 0.62 toward a value of 1 following grafting. In this study, the authors found that, when fast and slow muscles were reinnervated from a common nerve, maintenance of differences in rate of force development supported selective reinnervation, while loss of differences in time of force relaxation supported random reinnervation.

Skeletal muscle damage in the rat hindlimb following single or repeated daily bouts of downhill exercise.

This study was conducted to quantify and compare the extent of fibre degenerative and regenerative processes in different muscles of the rat hindlimb following single or repeated daily bouts of treadmill exercise. Wistar rats were used as non-exercised controls, or subjected to one, five, or ten (n = 8 per group), 30-minute daily bouts (-16 degrees, 12-15m.min-1) of downhill exercise. Soleus (S), vastus lateralis (VL), medial gastrocnemius (MG), plantaris (P), and tibialis anterior (TA) muscles were analyzed from transverse cryosections stained with either H&E for morphological alterations indicative of fibre degeneration or regeneration, or mATPase activity for determination of fibre type. Results showed that in all groups, the percentage of morphologically altered fibres (%AF) was greater in S (4-8%) than in MG, VL, P, or TA (1-2%). The %AF across all muscles was greater following only one, versus multiple exercise bouts, or versus no exercise. The proportions of AF of different histochemical types followed the same distribution as the fibre type in the muscle area examined. These direct assessments indicate that the extent of fibre degenerative and regenerative processes varies among the different muscles involved, and is greater following a single bout, compared to repeated daily bouts of exercise.

The distribution of centrosomes in endothelial cells of the rat aorta and inferior vena cava.

Centrosomes are preferentially oriented toward the heart in endothelial cells (ECs) of the pig aorta and pig and rabbit inferior vena cava (IVC). In the rabbit aorta this preferential orientation of the centrosome toward the heart decreases with age. To determine if this is also true in the rat, a species which is more amenable to experimental manipulation than the pig or the rabbit, we determined the position of centrosomes relative to the nucleus in ECs lining the aorta and IVC using whole mounts of vessels that were immunofluorescently stained with sera specific for centrosomes. In both the thoracic and abdominal aorta of the rat the majority of the ECs (60%) had centrosomes on the heart side of the nucleus, 25% had centrosomes on the side of the nucleus away from the heart and 15% had centrosomes in a central position in the cell. Similar results were obtained in the IVC of the rat where these values were, 58%, 31% and 11% respectively. A comparable preferential orientation of centrosomes toward the heart was also seen in the ECs of thoracic and abdominal aortas and IVCs of weanling and young adult rats and this did not decrease with age as it does in the rabbit aorta. When segments of the rat aorta were placed in organ culture, the percentage of ECs with preferentially oriented centrosomes decreased by 48 hrs, even though the cells remained elongated in shape. We have recently demonstrated that ECs in the rat aorta are normally migrating in the direction of the heart and thus in the direction in which the centrosomes in rat aortic ECs are preferentially oriented. This correlation is consistent with the general hypothesis that the centrosome position defines the direction of migration in monolayers of cells.

Reductions in sarcoplasmic reticulum Ca2+ ATPase activity in rat skeletal muscles of different fibre composition with ischemia and reperfusion.

To investigate the significance of fibre type and the duration of ischemia on changes in sarcoplasmic reticulum Ca2+ ATPase activity (SR Ca2+ ATPase), blood flow was occluded to the rat hind limb for 1, 2, or 3 h (n = 10 per group) and the soleus and extensor digitorum longus (EDL) muscles were examined following 2 h of reperfusion. When compared with the contralateral control muscles, calcium-dependent (total tau basal) SR Ca2+ ATPase activity in soleus was reduced (p < 0.05) to 75.9% by 1 h of ischemia and 2 h of reperfusion (13.1 +/- 0.6 vs. 9.95 +/- 0.85 mumol.mg-1 wet weight.min-1; X +/- SE) with no further reduction (p > 0.05) observed at either 2 h (9.75 +/- 0.57) or 3 h (9.40 +/- 0.64) of ischemia and 2 h of reperfusion. For the EDL muscles, SR Ca2+ ATPase activity with 2 h reperfusion was not reduced (p > 0.05) with 1 h of ischemia (80.4 +/- 3.0 vs. 70.7 +/- 2.9 mumol.mg-1 wet weight.min-1) but was reduced (66.7 +/- 2.3 mumol.mg-1 wet weight.min-1; p < 0.05) in the 2-h ischemia group, with further reductions (53.2 +/- 3.4 mumol.mg-1 wet weight.min-1; p < 0.05) in the 3-h ischemia group. No changes (p > 0.05) in basal or SR Mg2+ ATPase were found for either muscle group with ischemia and reperfusion, regardless of the duration of ischemia. When these results are interpreted in the context of the increases in SR Ca2+ ATPase activity that occur with ischemia, it appears that two components are involved in the reductions in SR Ca2+ ATPase activity noted during reperfusion: one that reduces the SR Ca2+ ATPase activity to below normal and one that simply reverses the ischemic-induced increase in SR Ca2+ ATPase activity. The former component appears to be more pronounced in the EDL muscle.

Metabolic and contractile responses of fast and slow twitch rat skeletal muscles to ischemia and reperfusion.

The purpose of this study was to investigate the significance of fiber type and the effects of the duration of ischemia on metabolic and contractile function of skeletal muscle. Under anesthesia, the distal tendons of the fast twitch extensor digitorum longus (EDL) and slow twitch soleus (SOL) muscles of the right hindlimb of female Wistar rats (250 to 300 gm) were connected to force transducers. Rats were assigned to group 1, 1 hour of ischemia; group 2, 2 hours of ischemia; or group 3, 3 hours of ischemia (n = 10 for each group). After ischemia, muscles were assessed for 2 hours of reperfusion. In both muscles, isometric twitch (Pt) and tetanus (Po) and 11 metabolic parameters were measured and compared with controls. After 1, 2, or 3 hours of ischemia Pt and Po were significantly (p < 0.05) lower than preischemic values. After 2 hours of reperfusion, forces and metabolic parameters of group 1 recovered to preischemic levels. However, contractile function of either muscle failed to recover fully after 2 hours of ischemia and 2 hours of reperfusion (SOL: Pt = 43.7 +/- 12 percent of initial; EDL: Pt = 32.2 +/- 9.2 percent) or after 3 hours of ischemia and 2 hours of reperfusion (SOL: Pt = 26.8 +/- 11 percent of initial; EDL: Pt = 19.3 +/- 6.8 percent). Although ADP and AMP recovered to preischemic levels in both muscles after 2 hours of ischemia and 2 hours of reperfusion, ATP recovered to just 70 percent in the soleus muscles (13.4 +/- 1.7 mmol/kg dry weight) and 60 percent in the extensor digitorum longus muscles (17.93 +/- 4.1 mmol/kg dry weight). After 3 hours of ischemia and 2 hours of reperfusion, ATP was further significantly (p < 0.05) decreased in the soleus muscles (48 percent initial) but not in the extensor digitorum longus muscles. Significant partial correlation coefficients (p < 0.005) were obtained between ATP levels and Pt (SOL: r = 0.757; EDL: r = 0.619) or Po (SOL: r = 0.810; EDL: r = 0.759). For this rat hindlimb model, we conclude that both fiber type and the duration of ischemia significantly affect metabolic and contractile function.

Relationship between the distribution of stress fibers and centrosomes in endothelial cells of the rat aorta.

Locomoting cells exhibit a polarity whereby certain organelles, like the centrosome, and cytoskeletal structures, like stress fibers, are preferentially oriented in the direction of migration. To determine if this was also true in endothelial cells (ECs) of the rat aorta that are migrating toward the heart, whole mounts of abdominal and thoracic aorta were double stained with rhodamine phalloidin to label stress fibers and sera that labels centrosomes. Our results show that in 66% of the ECs of the abdominal aorta where stress fibers were present, 47% had stress fibers on the heart side of the nucleus, 21% had stress fibers on the side of the nucleus away from the heart, and 32% had stress across the cell. Similarly, in 50% of the ECs of the thoracic aorta where stress fibers were present, these values were 56, 19, and 25%, respectively. The results also showed that the centrosome was preferentially located toward the heart in the majority (61%) of the ECs with stress fibers as well as in ECs without stress fibers. Since in both, the same percentage of ECs had centrosome preferentially oriented toward the heart, these results imply that while the centrosome may determine the position of the stress fibers, the stress fibers do not appear to determine the position of the centrosome. Nevertheless, both centrosomes and stress fibers in aortic ECs are preferentially oriented in the direction of migration, where they may be involved in defining the direction and providing the force of locomotion, respectively.

Ischemia-induced alterations in sarcoplasmic reticulum Ca(2+)-ATPase activity in rat soleus and EDL muscles.

To investigate the time-dependent effects of ischemia, as modified by muscle fiber type composition, on sarcoplasmic reticulum (SR) function, Ca(2+)-ATPase activity (total minus basal) was measured in homogenates prepared from samples obtained from rat soleus and extensor digitorum longus (EDL) muscle of ischemic and contralateral controls. Ischemia was induced by occlusion of blood flow to one hindlimb for periods of 1, 2, and 3 h (n = 10 per group). In EDL, maximal Ca(2+)-ATPase activity (expressed in mumol.g wet wt-1.min-1) was higher (P < 0.05) in ischemic than in control at 1 h (80 +/- 10 vs. 56.5 +/- 5.3) and increased progressively with ischemia at both 2 h (88 +/- 4.6 vs. 53.1 +/- 2.8) and 3 h (116 +/- 3.8 vs. 67.8 +/- 3.2). In contrast, in soleus, increases (P < 0.05) in Ca(2+)-ATPase activity with ischemia were observed at 2 h (19.2 +/- 0.86 vs. 14.0 +/- 0.56) and 3 h (19.9 +/- 1.4 vs. 12.4 +/- 0.62) but not at 1 h (10.7 +/- 1.5 vs. 10.0 +/- 0.83). In both EDL and soleus, basal Mg(2+)-ATPase was unchanged with ischemia. On the basis of these findings, it can be concluded that ischemia results in an increase in the maximal SR Ca(2+)-ATPase activity but that the time course of the change is dependent on the fiber type composition of the muscle.

Metabolic and contractile responses of fast- and slow-twitch rat skeletal muscles to ischemia.

Complete occlusion of blood flow to rat hind limb by tourniquet was used to study the effects of total ischemia for 1, 2, and 3 h on contractile function and metabolic behaviour of two muscles composed predominantly of either fast-twitch (extensor digitorum longus, EDL) or slow-twitch (soleus, SOL) fibres. Percent loss in twitch force (Pt) was greater (p < 0.05) in SOL than EDL during the first 45 min of ischemia. Following 1 h of ischemia, ATP concentration was lower (p < 0.05) than in the contralateral control (20.8 +/- 2.0 vs. 26.4 +/- 1.5 mmol/kg dry weight). Thereafter, the decline in ATP was greater, with approximately 95% depleted by 3 h of ischemia (1.46 +/- 0.46 mmol/kg dry weight). The effect of ischemia on ATP levels in the SOL was similar to ATP levels in the EDL, 1 h of ischemia also resulted in a large decrement in PCr, from 50.1 +/- 2.9 to 11.7 +/- 2.4 mmol/kg dry weight, and a large increase in lactate, from 25.0 +/- 3.0 to 114 +/- 10 mmol/kg dry weight. As ischemia was prolonged, only lactate was increased (p < 0.05) both at 2 h (171 +/- 12 mmol/kg dry weight) and 3 h (208 +/- 5.4 mmol/kg dry weight). Similar trends were found for SOL. By 3 h of ischemia, glycogen was depleted (p < 0.05) by 88% in EDL and 92% in SOL, respectively. These results support the hypothesis that both high energy phosphate transfer and anerobic glycolysis are of major importance in defending ATP hemostasis, particularly during the 1st h of ischemia, and that the resulting metabolic disturbances are responsible for the large fatigability observed. The mechanisms underlying the greater resistance to fatigue observed for the SOL compared with the EDL during the earlier period of ischemia remain uncertain.

Simultaneous assessment of isometric forces in fast- and slow-twitch muscles of single rat hindlimbs in situ.

An apparatus, consisting of a pair of small strain gauge transducers, was designed for the simultaneous assessment of isometric contractile function in two muscles, composed of a predominance of either fast- or slow-twitch fibers, and within a single rat hindlimb in situ. This facilitates assessment of mechanical performance of two separate muscles under identical conditions. In anesthetized rats (N = 10), the voltages and frequencies required to produce isometric twitch and tetanic forces from the soleus (SOL) and extensor digitorum longus (EDL) muscles were determined. The apparatus was then used to demonstrate the simultaneous assessment of forces produced by the SOL and EDL from the same hindlimbs (n = 5) during 30 min of fatigue and 30 min of recovery. With this apparatus, data collected were comparable to published data. The apparatus can be used for the simultaneous assessment of isometric contractile function and fatigue in both a fast- and a slow-twitch muscle of a single rat hindlimb in situ.

Recovery of synergistic skeletal muscle function following ischemia.

This study tests the hypothesis that if the fast twitch muscles in a synergistic group were more susceptible to ischemia/reperfusion injury, then the slow twitch muscle would compensate functionally during recovery. Rat hindlimb fast twitch gastrocnemius and plantaris muscles and slow twitch soleus muscle were studied. In the experimental (E) group of rats, the right hindlimbs had 2 hr of pressure-controlled (300 mmHg) tourniquet ischemia. The masses and the maximal isometric tetanic forces of the three muscles were evaluated at 1, 3, 5, and 7 weeks in E (n = 24) and a control (C) group of rats (n = 24). Gastrocnemius mass and plantaris mass were both reduced (at 1, 3, and 5 weeks and at 1 and 3 weeks, respectively), whereas there were no significant changes in the mass of the soleus. The maximal isometric tetanic forces (N) measured at 1 week of recovery were reduced to 52, 53, and 67% of C values for the gastrocnemius, plantaris, and soleus, respectively. However, at 1 week the normalized isometric tetanic forces (N/g) for all three muscles were reduced to 66-69% of the C values. By Week 3, the tetanic forces (N or N/g) of all muscles had recovered to control values. On average, the gastrocnemius, plantaris, and soleus muscles of the C groups contributed 68, 24, and 8%, respectively, of the total synergistic tetanic force. These values were unaffected by ischemia. From this experiment, it is concluded that 2 hr of tourniquet ischemia resulted in a selective decrement in mass of the fast twitch muscles.(ABSTRACT TRUNCATED AT 250 WORDS)