Neuromuscular fatigue and potentiation following two successive high intensity resistance exercise sessions.

Resistance exercise can result in both potentiating and fatiguing responses. These responses can acutely affect performance, which may affect subsequent exercise sessions in the same day. The purpose of this investigation was to study the acute neuromuscular responses to two high intensity training sessions in the same day. Twelve recreationally trained males performed two training sessions, each involving ten sets of five repetitions in the speed squat exercise. For the initial session (HIT-1), the barbell load was constant at 70% one repetition maximum, whereas during the second session (HIT-2), barbell load decreased if movement velocity decreased. Neuromuscular performance testing consisted of unilateral isometric knee extensor actions performed prior to the training day (PRE) and following each testing session. Prior to the sessions, subjects provided a muscle biopsy for myosin heavy chain analysis. Peak force was impaired 16.9 (9.5)% (P approximately 0.00; d=1.62) following HIT-1 and 19.9 (18.4)% (P approximately 0.00; d=1.94) following HIT-2. Initial rate of force development was depressed from PRE following HIT-1 (P approximately 0.00; d=1.74) and HIT-2 (P approximately 0.00; d=2.18); however, this was dependent on muscle fiber composition. Significant correlations existed between the change score for initial rate of force development from HIT-1 to HIT-2 and myosin heavy chain I (r= -0.60; P=0.04) and IIa (r=0.69; P=0.01) expression. Impaired neuromuscular performance following HIT-1 may occur due to low frequency fatigue. For individuals with predominantly myosin heavy chain IIa, HIT-2 appeared to induce post-activation potentiation, resulting in restoration of the initial rate of force development.

The effects of high-intensity exercise on a 10-second sprint cycle test.

Nine men (25.11 +/- 1.16 years) performed 3 different test sessions. In the control session, subjects performed a 10-second sprint cycle test and 1 repetition maximum (1RM) in the back squat. The 5-minute test session consisted of 10 x 1 repetition in the parallel back squat exercise at 90% of their 1RM, 5 minutes of rest, and then a 10-second sprint cycle test. The 20-minute test session consisted of the same test protocol as the 5-minute test session except that the subjects rested for 20-minutes prior to the sprint cycle test. Significant differences were found in average power and average power relative to body weight (F = 5.684, p = 0.014, and F = 1.258, p = 0.006, respectively) for the 5-minute test session. The authors conclude that this particular squat protocol could have a potential carry-over effect into improvements in 100-m sprint times when performing the squats 5-minutes prior to performance.

Multiple-joint velocity-spectrum strength/power development consequent to repetition manipulation.

BACKGROUND: Various repetition strategies are employed in typical weight-training programs. Strength is purportedly best developed using relatively few repetitions against great resistance. Strength in this context has typically been measured isotonically (dynamic constant external resistance or DCER) by performing a one-repetition maximum (1 RM). Multiple-joint isokinetic (velocity controlled) strength assessments are now available which may enable us to emulate movement patterns and velocities with those occurring in everyday activities while providing us with force and power information that heretofore has been difficult to obtain. Therefore, we assessed the effects of various repetition schemes during heavy-resistance training on multiple-joint isokinetic performance. METHODS. SETTING: Volunteers participated in 12 weeks (36 sessions) of variable-resistance weight training (8 different exercises) in one of the following programs: I-3 sets x 3-4 RM; II-3 x 9-10 RM; III-3 x 15-16 RM; IV, control. PARTICIPANTS: 48 apparently-healthy young men (18 to 34 years of age, X = 23.2) who had not participated in systematic heavy-resistance training during the previous year. MEASURES: Pre and post velocity-spectrum tests were conducted for both the squat (0.41, 0.65, 0.90, 1.14, and 1.39 m x s(-1) and bench press (0.50, 0.79, 1.09, 1.39 and 1.69 m x s-1) at which time peak force and peak power were measured. Force and power measurements were adjusted to control for body weight (N/kg and W/kg, respectively). Change (delta) scores were used for comparisons. RESULTS: One-way ANOVA s indicated that when compared to controls, improvements in force were significantly (p < 0.05) greater only at the slowest velocity (squats: Group II > Control; bench presses: Groups I, II, III > Control). However, changes in power were significantly (p < 0.05) greater than for controls at all 5 velocities tested (squats: Groups I, II > Control; bench presses: Groups I, II > Control except at 1.69 m x sec-1) where only Group I > Control). CONCLUSIONS: Due to the mixed findings for force improvements consequent to the various repetition schemes, conclusions are somewhat tentative. It appears, however, that strength increases only for slow velocities in young, previously untrained men consequent to 3 months of a relatively wide range of RM schemes using variable-resistance equipment. Power, on the other hand, appears to increase in the same subjects across a velocity spectrum for both squats and bench presses when no more than 10 RM are performed per set.

Gross measures of exercise-induced muscular hypertrophy.

STUDY DESIGN: Pretest-posttest, single factor design. OBJECTIVES: To compare several indices that might be used to depict muscle size. BACKGROUND: The particular strategy used during heavy-resistance training may determine the magnitude of hypertrophic adaptations. At the same time, assorted measures supposedly reflecting muscle size may provide different results. METHODS AND MEASURES: Four groups of men (n = 38, mean age = 21.1 years, SD = 2.1) were exposed to conditions designed to elicit differential hypertrophic adaptations following 21 sessions of squat training. Three of the groups performed 4 sets of multiple repetitions maximum (RM): group I, 3-5 RM; group II, 13-15 RM; and group III, 23-25 RM. A control (C) group did no formal physical training. Tests used to represent muscle size included body weight, thigh girth, net thigh girth, and quadriceps femoris and hamstring thicknesses via B-mode ultrasound. RESULTS: Changes in the groups subsequent to training were similar for body weight and hamstring thickness. Results differed for the remaining 3 dependent variables (mean +/- SD): thigh girth was greater in groups II (1.42 +/- 1.00) and III (1.35 +/- 1.16) than in group C (0.24 +/- 0.69); net thigh girth was greater in groups II (1.33 +/- 0.77) and III (1.40 +/- 1.03) than in group C (0.10 +/- 0.84); and quadriceps femoris thickness was greater in all 3 training groups (I, 0.61 +/- 0.54; II, 0.43 +/- 0.30; III, 0.55 +/- 0.39) than in group C (0.05 +/- 0.11). CONCLUSIONS: Observed muscle mass change following heavy-resistance training is dependent upon both the training intervention and tool used for measurement.

Effects of heavy-resistance triceps surae muscle training on strength and muscularity of men and women.

The purpose of this study was to determine selected functional and structural effects of heavy-resistance training on the triceps surae muscles of men and women. We pretested 28 men and 28 women for triceps surae muscle isotonic strength and muscularity after five practice sessions that familiarized them with the study equipment. Triceps surae muscle isotonic strength was determined using a 1-repetition maximum seated heel raise. Muscularity involved the measurement of relaxed lower leg circumference and net circumference and ultrasonically determined triceps surae muscle thickness. Twenty-eight subjects (14 men, 14 women) were selected randomly after pretesting to participate in 24 sessions of standardized weight training primarily involving the triceps surae muscles, and the remaining subjects (14 men, 14 women) served as nontraining controls. After eight weeks of training, triceps surae muscle isotonic strength had increased significantly (p less than .001) for both men and women in the Treatment Group when compared with the Control Group. No other dependent variables changed significantly. We concluded that eight weeks of heavy-resistance training involving the triceps surae muscles elicits similar significant increases in isotonic muscle strength in both men and women without concurrent increases in muscularity.

Three protocols for measuring subcutaneous fat thickness on the upper extremities.

Three protocols for measuring subcutaneous fat thickness were compared and their level of association determined in young adults. Subjects included 21 men and 21 women, 18-24 years of age. Skinfold calipers, A- and B-mode ultrasound were used to measure the thickness of the subcutaneous fat layer overlying the anterior and posterior aspects of the upper arm. Each protocol was independently administered within a 30-min block of time in a randomly rotated sequence. Significant differences (p less than 0.05) between protocols were observed depending upon site of measurement and gender of the subject. At both the anterior and posterior sites for men, B-mode and halved skinfold were similar but significantly less than A-mode measurements. At the anterior site for women, A-mode and skinfold were similar but significantly greater than B-mode measurements. At the posterior site for women, all three measurements were similar. Correlations between the protocols were positive with men's levels ranging from 0.59 to 0.74, while women's levels were from 0.39 to 0.89. It was concluded that although skinfold calipers, A-mode ultrasound, and B-mode ultrasound may be used to obtain moderately associated measurements of upper-arm subcutaneous fat thickness in young adults, the three protocols yield inconsistently similar data.

Upper extremity assessment of muscularity in young children.

An investigation involving 16 boys and 16 girls, 7 to 9 years of age, was conducted for the following purposes: to assess the reliability of an ultrasonic procedure for measuring skeletal muscle thickness at two sites on the upper arm; and to determine the association between these ultrasonic measurements and corresponding circumference and net circumference measures in children. B-mode ultrasound was used to determine muscle thickness at both arm sites. A controlled-tension Gulick tape was used for circumference measures, and skinfold calipers were used to obtain the correction factor for the net circumference measurement. Reliability coefficients (intraclass correlations) were high for sonograms at both the anterior and posterior sites. Associations (Pearson correlations) between muscle sonograms and arm circumference measures were moderately high in boys and low to moderate in girls. It was concluded that anterior and posterior upper arm muscle sonograms can be reliably obtained in young children for scans repeated within 30 minutes. It was also concluded that arm circumference measures are more highly associated with corresponding muscle sonograms in boys than in girls. J Orthop Sports Phys Ther 1987;8(8):397-401.

Ultrasonic protocols for separately measuring subcutaneous fat and skeletal muscle thickness in the calf area.

Information regarding the use of brightness-mode (B-mode) ultrasound for separately measuring the thickness of subcutaneous fat and skeletal muscle in the calf area was evaluated. Subjects were volunteers, 32 men and 32 women college students. Fat was measured with skinfold calipers and B-mode ultrasound. We used calf circumference and B-mode ultrasound simultaneously to assess muscle size. Ultrasonic measurements of both fat and muscle were repeated within 30 minutes to evaluate reliability. Men were 24 percent heavier than women but had a thinner fat layer as measured by skinfolds (49%) and ultrasound (29%). Men also had a relatively larger calf muscle as assessed by circumference (7%) and ultrasound (29%). Intraclass correlation coefficients were no less than .99 for repeated ultrasonic measurements of both fat and muscle for men and women; therefore, these procedures are reliable for at least a short period of time. Associations between skinfolds and fat sonograms were high in men (r = .87) and moderate in women (r = .50). Associations between circumferences and muscle sonograms were moderately high in both men (r = .80) and women (r = .76). All four associations were statistically significant (p less than .05).

Giant melanosomes in multiple lentigines syndrome.

Biopsy specimens of normal skin and lentigines from an 82-year-old man with multiple lentigines syndrome were examined with light and electron microscopes. Giant melanosomes were found in dermal melanophages, melanocytes, and keratinocytes in all epidermal layers. Morphologic characteristics of these melanosomes are described, and other conditions in which they have been found are discussed.

Effects of topical fluorouracil on normal skin.

Daily application of 1% fluorouracil cream to normal white skin results in definite morphologic alterations of the epidermis. Although clinical changes were not present, electron microscopic examination of the tissue demonstrates changes especially pronounced in the epidermal keratinocytes. These changes consist of cytoplasmic vacuoles, alterations in the mitochondria, Golgi complex, and endoplasmic reticulum, as well as widened extracellular spaces.

Embryology of the epidermis: ultrastructural aspects. II. Period of differentiation in the mouse with mammalian comparisons.

A detailed light and electron microscopic study of the cellular morphology of the epidermis in the 13 through 16 day mouse fetus reveals that an occasional intermediate cell is interposed between the basal and peridermal layers on day 13. All layers are mitotically active. Tonofilaments, unassociated with desmosomes, are present within the basal cell cytoplasm and the mitotic axis of the basal cells has changed from a parallel to a perpendicular plane with respect to the epidermal surface. At 14 days, a complete stratum intermedium, composed of one or two cell layers, is present. Rarely, developing hemidesmosomes are observed. Pools of glycogen are present in all cells below the periderm. The periderm is dense and no longer mitotically active. The skein of filaments, present in the inferior cytoplasmic region of the basal cells on days 12 and 13, is now absent. In the 15 day fetus, numerous developing hemidesmosomes are present. The stratum intermedium contains three to four layers of cells, and filaments are located deep within the cytoplasm of these intermediate cells. Rarely, a few developing keratohyalin granules and keratinosomes are present. A stratum intermedium is no longer present in the 16 day fetus. This region is now composed of a stratum spinosum and a stratum granulosum. Numerous keratinosomes are located in the upper stratum spinosum and lower stratum granulosum. The cells in the stratum granulosum are nucleated and the uppermost cells contain large keratohyalin granules. Three heterogeneous and one homogeneous type of keratohyalin granule is described. Dense bodies are present within mitochondria, nuclei, glycogen pools and the peridermal cytoplasm. The periderm is no longer dense and glycogen and keratohyalin granules are not observed in this layer.

Embryology of the epidermis: ultrastructural aspects. III. Maturation and primary appearance of dendritic cells in the mouse with mammalian comparisons.

The epidermis of mice ranging in age from prenatal day 17 through postnatal day 4 and, in addition, postnatal day 18, was studied with the electron microscope. In the 17 day fetus, the periderm may or may not be present and a stratum corneum is developing in the latter case. The cells of the strata spinosum and granulosum contain much glycogen and many keratinosomes and homogeneous keratohyalin granules which appear to line up in a row near the distal cell membranes, fuse and form keratinized cells which contain material similar in density to that of the individual keratohyalin granules. In the 18 to 20 day fetuses, no periderm is present. The stratum corneum becomes well-developed. The quantity of glycogen decreases but the number of keratinosomes and keratohyalin granules increases. Some cells in the basal region contain necrotic phagocytosed cells. Few changes occur in the epidermis of the neonate, although the stratum corneum increases in thickness. In the early postnatal period, the mouse epidermis is mature in appearance and resembles that of man. By postnatal day 18, the whole epidermis is much thinner, although all classical strata can usually be identified. The primary appearance and subsequent maturation of epidermal dendritic cells was also studied in the mouse during the embryonic, fetal, early postnatal and 18 day postnatal periods. Melanocytes which lacked cell processes were first identified in the 15 day fetus. Melanocyte cell processes and an increasing number of melanosomes, as well as melanocytes, are present between prenatal day 18 and postnatal day 3. On postnatal day 4, fewer melanocytes are present and they contain vacuoles. Phagocytosed melanocytes are also present within basal keratinocytes. Undifferentiated dendritic cells or indeterminate cells are observed beginning on prenatal day 16. These cells do not appear to increase significantly in number subsequently. On postnatal day 18, Langerhans cells and indeterminate cells are present but no melanocytes can be identified. No Merkel cells were observed. Mitotic dendritic cells or dendritic cells traversing the basal lamina were not observed.

Embryology of the epidermis: ultrastructural aspects. 1. Formation and early development in the mouse with mammalian comparisons.

A detailed light and electron microscopic study of the cellular morphology of developing epidermis in the 7 to 12 day mouse embryo reveals that a single layer of ectoderm is not present until day 8. The 8-day embryonic epithelium is characterized by the presence of microvilli, apical attachment specializations, developing desmosomes and a thin, immature basal lamina. The 9-day embryonic epithelium is flatter and has both an increased number of microvilli on the surface and an increased number of microtubules in association with developing desmosomes. On day 10, numerous developing desmosomes are associated with fine filaments in the regions of the attachment plaques. Occasional peridermal cells are present on day 11. Numerous granules are associated with the inferior cell membranes of the superficial or uppermost cell processes. In the 12-day embryo, the periderm forms a complete layer. A skein of fine filaments is present just inside the basal cell membrane of the germinative cells and microtubules are more abundant in the basal cell cytoplasm.