Todd A. Miller

Acute Effects of Static, Dynamic, and Proprioceptive Neuromuscular Facilitation Stretching on Muscle Power in Women

Manoel, ME, Harris-Love, MO, Danoff, JV, and Miller, TA. Acute effects of static, dynamic, and proprioceptive neuromuscular facilitation stretching on muscle power in women. J Strength Cond Res 22(5): 1528-1534, 2008-The purpose of this study was to investigate the acute effects of 3 types of stretching-static, dynamic, and proprioceptive neuromuscular facilitation (PNF)-on peak muscle power output in women. Concentric knee extension power was measured isokinetically at 60°·s-1 and 180°·s-1 in 12 healthy and recreationally active women (mean age ± SD, 24 ± 3.3 years). Testing occurred before and after each of 3 different stretching protocols and a control condition in which no stretching was performed. During 4 separate laboratory visits, each subject performed 5 minutes of stationary cycling at 50 W before performing the control condition, static stretching protocol, dynamic stretching protocol, or PNF protocol. Three submaximal warm-up trials preceded 3 maximal knee extensions at each testing velocity. A 2-minute rest was allowed between testing at each velocity. The results of the statistical analysis indicated that none of the stretching protocols caused a decrease in knee extension power. Dynamic stretching produced percentage increases (8.9% at 60°·s-1 and 6.3% at 180°·s-1) in peak knee extension power at both testing velocities that were greater than changes in power after static and PNF stretching. The findings suggest that dynamic stretching may increase acute muscular power to a greater degree than static and PNF stretching. These findings may have important implications for athletes who participate in events that rely on a high level of muscular power.

Mechanisms of force loss in diabetic mouse skeletal muscle.

Pathologic changes to α‐motoneurons may contribute to decreases in skeletal muscle strength in diabetes. The present study examines this possibility. Female ICR mice (∼25 g) were given a single injection of streptozotocin (200 mg/kg). After 2, 4, and 8 weeks of diabetes, we measured maximum isometric tetanic torque of the fast‐twitch anterior crural muscles at the ankle when stimulated through the common peroneal nerve, and maximal isometric tetanic force in the directly stimulated extensor digitorum longus (EDL) muscle. After 4 weeks, the relative loss of torque via nerve stimulation (−43%) was greater (P = 0.02) than the force loss in the directly stimulated muscle (−24%), indicating a functional neural deficit. However, the percent changes in strength in these two methods of stimulation were not different (P = 0.41) in the 8‐week diabetic animals, indicating that functional impairment resided in the muscle. This suggests an early distal motoneuron or neuromuscular junction deficit that improved as the intrinsic muscle deficit worsened. Preliminary evidence also suggests excitation–contraction uncoupling may contribute to the loss of strength in fast‐twitch muscles. Muscle Nerve 28: 493–500, 2003

Fiber Composition and Oxidative Capacity of Hamster Skeletal Muscle

The hamster is a valuable biological model for physiological investigation. Despite the obvious importance of the integration of cardiorespiratory and muscular system function, little information is available regarding hamster muscle fiber type and oxidative capacity, both of which are key determinants of muscle function. The purpose of this investigation was to measure immunohistochemically the relative composition and size of muscle fibers composed of types I, IIA, IIX, and IIB fibers in hamster skeletal muscle. The oxidative capacity of each muscle was also assessed by measuring citrate synthase activity. Twenty-eight hindlimb, respiratory, and facial muscles or muscle parts from adult (144–147 g bw) male Syrian golden hamsters (n=3) were dissected bilaterally, weighed, and frozen for immunohistochemical and biochemical analysis. Combining data from all 28 muscles analyzed, type I fibers made up 5% of the muscle mass, type IIA fibers 16%, type IIX fibers 39%, and type IIB fibers 40%. Mean fiber cross-sectional area across muscles was 1665 ± 328 μm2 for type I fibers, 1900 ± 417 μm2 for type IIA fibers, 3230 ± 784 μm2 for type IIX fibers, and 4171 ± 864 μm2 for type IIB fibers. Citrate synthase activity was most closely related to the population of type IIA fibers (r=0.68, p<0.0001) and was in the rank order of type IIA > I > IIX > IIB. These data demonstrate that hamster skeletal muscle is predominantly composed of type IIB and IIX fibers.

Comparison of acute exercise responses between conventional video gaming and isometric resistance exergaming.

Bonetti, AJ, Drury, DG, Danoff, JV, and Miller, TA. Comparison of acute exercise responses between conventional video gaming and isometric resistance exergaming. J Strength Cond Res 24(7): 1799-1803, 2010-Exergaming is a relatively new type of entertainment that couples physical activity and video gaming. To date, research that has focused on the physiologic responses to exergaming has been focused exclusively on aerobic-type activities. The purpose of this project was to describe the acute exercise responses (i.e., oxygen uptake [&OV0312;O2], heart rate, and rate of perceived exertion [RPE]) to exergaming using full-body isometric muscle resistance and to determine whether these responses are different during single- versus opponent-based play. Male subjects (n = 32) were randomly and equally divided into either an experimental (EXP) or control (CON) group. Acute exercise responses (&OV0312;O2, heart rate, and RPE) were measured in all subjects during both solo- and opponent-based video game play. Subjects in the EXP group played using a controller that relied on full-body isometric muscle resistance to manipulate the on-screen character, whereas CON subjects used a conventional handheld controller. During solo play, the EXP group exhibited significantly higher values for &OV0312;O2 (9.60 ±0.50 mL/kg/min) and energy expenditure (3.50 ± 0.14 kcal/min) than the CON group (&OV0312;O2 5.05 ± 0.16 mL/kg/min; energy expenditure 1.92 ± 0.07 kcal/min). These changes occurred with no significant differences in RPE or heart rate between the groups. These results suggest that whole-body isometric exergaming results in greater energy expenditure than conventional video gaming, with no increase in perceived exertion during play. This could have important implications regarding long-term energy expenditure in gamers.

The effects of multiaxial and uniaxial unstable surface balance training in college athletes.

Eisen, TC, Danoff, JV, Leone, JE, and Miller, TA. The effects of multiaxial and uniaxial unstable surface balance training in college athletes. J Strength Cond Res 24(7): 1740-1745, 2010-The purpose of this study was to compare the effects of 2 different types of unstable surface balance training (uniaxial on a rocker board [RB] and multiaxial on a dynadisc [DD]) on balance in division 1 collegiate athletes in sports that are at high risk for ankle sprains. Subjects (n = 36) consisted of male soccer players and female volleyball and soccer players who were equally and randomly assigned to 1 of 3 groups (CON, DD, and RB). Balance training consisting of balancing on 1 leg on either the RB or DD, while repeatedly catching a 1-kg ball was performed 3 times per week for 4 weeks. Balance was tested with the Star Excursion Balance Test (SEBT) before, halfway through, and at the completion of the balance training. Control (CON) subjects also were given the balance test but did not participate in the training. A 3-way repeated analysis of variance revealed that no group individually changed SEBT scores from pre (CON, 0.98 ± 0.086; DD, 0.98 ± 0.083; RB, 0.97 ± 0.085) to post (CON, 1.00 ± 0.090; DD, 1.01 ± 0.088; RB, 1.02 ± 0.068) after balance training. When the 2 treatment groups were combined (DD and RB), the p value decreased and came closer to significance (p = 0.136). When all 3 groups were combined, there was a significant difference in SEBT scores from pretraining (CON + DD + RB; 0.98 ± 0.085) to posttraining (CON + DD + RB; 1.01 ± 0.082), which likely indicates low statistical power. The increase in physical activity the subjects experienced during the return to in-season activity, may have contributed to the significant differences in SEBT scores over time but not between DD or RB training. Therefore, a threshold level of physical activity may exist that is necessary to maintain balance during the off-season.

Immunohistochemical fiber typing of harbor seal skeletal muscle

SUMMARY There is strong evidence that pinnipeds maintain a lipid-based, aerobic metabolism during diving. However, the few fiber-typing studies performed on pinniped skeletal muscles are not consistent with an aerobic physiological profile. The objective of this study was to reexamine the fiber type distribution throughout the primary locomotory muscles of the harbor seal Phoca vitulina. Results from immunohistochemical (IHC) fiber typing indicated that harbor seal swimming muscles (the epaxial muscles) are composed of 47.4% type I (slow twitch, oxidative) fibers and 52.8% IIa (fast twitch, oxidative) fibers, which are homogeneously distributed throughout the muscle. Harbor seal pectoralis, a secondary swimming muscle, was composed of 16.2% type I and 84.3% type IIa fibers. No fast twitch, glycolytic (type IIb) fibers were detected in either muscle, in contrast to published data on fiber typing of harbor seal epaxial muscles using traditional histochemical techniques. The extreme specificity inherent in the IHC fiber typing procedure leads us to conclude that harbor seal swimming muscle is entirely composed of oxidative fibers. Our results are consistent with the enzymatic analyses of pinniped skeletal muscle that support the use of lipid-derived aerobic catabolism to fuel working muscle during diving in these marine mammals.

The Effects of Concurrent Endurance and Resistance Training on 2,000-m Rowing Ergometer Times in Collegiate Male Rowers

Gallagher, D, DiPietro, L, Visek, AJ, Bancheri, JM, and Miller, TA. The effects of concurrent endurance and resistance training on 2,000-m rowing ergometer times in collegiate male rowers. J Strength Cond Res 24(5): 1208-1214, 2010-The current study evaluated if high rep, low rep, or no weight training at all would be best suited for decreasing 2,000-m rowing ergometer times in male varsity rowers. Subjects (n = 18) were rowers from Grand Valley State University who were randomly and equally assigned to 1 of 3 groups: control (CON), high-load low repetitions (HLLR), and low-load high repetitions (LLHR). The weight training groups resistance trained and rowed twice a week, whereas the control group only rowed twice a week. Each group performed the training study workouts (weight training and rowing) along with their daily prescribed varsity practices. The subjects performed both pre and post 2,000-m ergometer tests on concept 2 indoor rowers to evaluate the effects of each training protocol. Paired t-tests revealed statistically significant decreases in 2,000-m times from pre to posttesting for all groups (p < 0.05), whereas a 1-way analysis of variance with repeated measures did not reveal a statistically significant difference (p < 0.96) between the 3 groups (ΔCON: −2.8%, ΔLLHR: −3.1%, and ΔHLLR: −3.5%). However, a trend existed in the hypothesized direction, as the HLLR illustrated the greatest decrease in mean rowing time (CON: 11 seconds, LLHR: 12 seconds, and HLLR: 15 seconds). Overall, the current study demonstrates that although weight training does not create a statistically significant short-term training effect on rowing performance, the profound decreases in 2,000-m times seen in this study may be of practical significance for the oarsman.

Older adult perceptions of the physicians’ role in promoting physical activity

Purpose: The purpose of this research was to explore the perceptions of independent living older adults regarding their physicians’ role in promoting physical activity (PA). Methods: A qualitative inductive analysis was undertaken using focus group discussions of independent living adults over age 60. Thirty-one participants were placed into focus groups based on their current level of PA (three focus groups of physically active persons, and three focus groups of physically inactive persons). Discussions were audiotaped and transcribed verbatim. Qualitative data were open and axially coded and independently analysed by two researchers for emergent themes. Inter-rater reliability was established (κ = 0.89). Results: Themes for physically active and physically inactive groups included limited or inadequate discussions with their physician regarding PA, and the use of PA as a secondary prevention method. The physician as an extrinsic motivator of PA emerged only in the physically active group discussions. Some participants believed that their physician was uncomfortable discussing PA or that their physician was unable to provide them with sufficient PA guidelines. When PA counseling occurred, it was usually in relation to a preexisting illness. Discussion and conclusion: Although participants were looking to their physician for PA counseling, physicians were not initiating a regular PA dialogue. Possible reasons may include lack of physician knowledge or skill. Further research is needed to explore physicians’ knowledge and comfort when prescribing exercise or PA for their patients. Implications for Rehabilitation Physical activity and exercise are essential to maintain good health and prevent disease. Physicians can play an important role in promoting physical activity. In this small qualitative study, older adults perceived their exercise conversations with their physician as inadequate or only related to preexisting conditions. All health care providers should take collective responsibility for encouraging healthy life style choices including regular physical activity and exercise.

Development of a Rowing-Specific Oo2max Field Test

Huntsman, HD, DiPietro, L, Drury, DG, and Miller, TA. Development of a rowing specific &OV0312;o2max field test. J Strength Cond Res 25(6): 1774-1779, 2011—The purpose of this study was to develop an aerobic capacity test for rowers using minimal equipment that could be used in the field. Thirty rowers (15 men and 15 women) between the ages of 18 and 26 years were recruited on a volunteer basis from the District of Columbia metro area. The testing protocol consisted of a maximum of 7 2-minute stages on a rowing ergometer, separated by 30-second breaks where lactic acid concentrations were analyzed. Starting intensity for men was 200 W, although women started at 150 W, and each stage increased by 50 W. Expired gasses were collected during the test, and athletes were asked to row until maximal volition so that the directly measured &OV0312;o2max could be compared to predicted values. Peak heart rates from each completed stage were plotted, and regression equations were calculated to predict &OV0312;o2max. Separate regression equations were calculated for men and women. The predicted &OV0312;o2max values were approximately 23 and 25% lower than what was actually achieved for men and women, respectively. Heart rate was a stronger correlate of &OV0312;o2max in men compared with in women. Among men, we observed a moderate and statistically significant correlation (r = 0.55; p = 0.05), whereas among women, no such agreement was observed (r = −0.05; p > 0.85). The principle finding of this study was that the test was adequate in predicting &OV0312;o2max in men but was inadequate in its prediction in women. With slight modifications to the testing protocol, stronger correlations and a more accurate prediction of &OV0312;o2max is expected in men.

Influence of Upper-body External Loading on Anaerobic Exercise Performance

Inacio, M, Dipietro, L, Visek, AJ, and Miller, TA. Influence of upper-body external loading on anaerobic exercise performance. J Strength Cond Res 25(4): 896-902, 2011-The purpose of this study was to assess the threshold where simulated adipose tissue weight gain significantly affects performance in common anaerobic tasks and determine whether differences exist between men and women. Forty-six subjects (men = 21; women = 25) were tested for vertical jump, 20- and 40-yd dash, and 20-yd shuttle tests under 6 different loading conditions (0, 2, 4, 6, 8, and 10% of added body weight). Results were compared to each subjects baseline values (0% loading condition). Results demonstrate significant decrements in performance, starting at the 2% loading condition, for both genders, in every performance test (p < 0.05). On average, subjects jumped 4.91 ± 0.29 to 9.83 ± 0.30 cm less, increased agility test times from 5.49 ± 0.56 to 5.86 ± 0.61 seconds, and increased sprint times from 7.80 ± 0.96 to 8.39 ± 1.07 seconds (2-10%, respectively; p < 0.05). When lower-body power was corrected for total body mass, men exerted significantly more power than women did in every loading condition. Conversely, when lower-body power was corrected for lean body mass, men exerted significantly more power than did women only at the 2% loading condition. This study demonstrates that for the specific anaerobic performance tests performed, increases in external loading as low as 2% of body weight results in significant decreases in performance. Moreover, for these specific tests, men and women tend to express the same threshold in performance decrements.