While bones and muscles adapt to mechanical loading, it appears that very specific types of stimuli must be applied to achieve osteogenesis. Our study assessed musculoskeletal outcomes to 30 training sessions on an Inertial Exercise Trainer (Newnan, GA). Subjects (n=13) performed workouts with their left leg, while their right served as an untreated control. Workouts entailed three 60-s sets each of knee extension, hip extension and calf press exercises, separated by 90-s rests. Before and after the 30 training sessions, subjects underwent strength tests (knee and ankle extensors of both legs), DEXA scans (hip, knee and ankles of both legs), and blood draws. After 30 training sessions 2×2 ANOVAs showed left leg peak torques rose significantly. 2×2 ANCOVAs, with bone scan area as a covariate, showed significant left leg calcaneal bone mineral content (+29%) and density (+33%) increases after 30 training sessions. A significant decline in C-terminal telopeptides of type I collagen, a blood marker of bone resorption, also occurred after 30 training sessions. The Inertial Exercise Trainer's large volume of training session repetitions elicited high peak force, peak acceleration and impulses that likely provided a mechanical loading stimulus that evoked calcaneal accretion.

Chen, L, Davison, SW, Selimovic, EA, Mueller, RE, Beatty, SR, Carter, KA, Parmar, PJ, Symons, TB, Pantalos, GM, and Caruso, JF. Load-power relationships for high-speed knee extension exercise. J Strength Cond Res 33(6): 1480–1487, 2019—Seventy subjects did 4 knee extensor workouts with their left legs to assess load-power relationships produced on a high-speed trainer (HST; Newnan, GA, USA). Each workout is composed of 4 sets done on the HST at a different load (1, 4.4, 6.7, 9 kg). A Latin Squares Design determined load sequence per workout. Average power (AP) and peak power (PP) and those same values normalized to body mass (BM) and fat-free mass (AP/BM, PP/BM, AP/FFM, PP/FFM) were each analyzed with 2 (gender) × 4 (load) analysis of variances, with repeated measures for load. We assessed relationships between normalized loads and AP and PP values with correlation coefficients. Average power results revealed a significant interaction, with men > women at 9 kg. Peak power/body mass also yielded an interaction, with women > men at 6.7 and 9 kg. Average power/fat-free mass and PP/FFM each produced interactions, with women > men at 4.4, 6.7, and 9 kg. Correlation coefficients showed significant (r = 0.80–0.82) relationships between normalized loads and AP and PP values. In conclusion, the very low inertial resistance to initiate each repetition on this novel device may in part explain our PP/BM, AP/FFM, PP/FFM results, in which higher values were achieved by women. Our practical applications imply that the low inertial resistance for HST repetitions negates male size and strength advantages typically seen when power is measured.

Subjects (n=13) did 30 workouts with their left leg on an Inertial Exercise Trainer (IET), while their right leg served as an untreated control. Before and after the 30 workouts, they underwent isokinetic strength tests (knee and ankle extensors of both legs) whose peak torque (PT), time to PT (TTPT), and rate of torque development (RTD) values were each analyzed with 2(leg)×2(time)×3(velocity) analysis of variances (ANOVAs), with repeated measures per independent variable. Peak force (PF) and total work (TW) data were measured from each IET workout, and they represent time course strength changes produced by our exercise intervention. PF and TW values for the three IET exercises that comprised each workout were each analyzed with one-way ANOVAs with time as the independent variable. Results included significant ankle and knee extensor PT increases, whereby the left leg achieved higher values at posttesting, but there were no significant TTPT changes and a time effect for ankle extensor RTD. Our data show that PF and TW each had significant increases over time, with the latter exhibiting greater gains over the 30-workout intervention. Our results imply that the IET yields strength gains over time comparable to standard resistive exercise hardware.

Lower leg exercises are impacted by the anatomy of the triceps surae-Achilles tendon complex. Such exercises may utilize series elastic energy (SEE), temporarily stored within the Achilles tendon, to augment forces exerted by the triceps surae. While SEE's contribution to bipedal jumping and walking have been assessed, other lower leg exercises yet to receive similar scrutiny include seated calf presses done on flywheel-based hardware. Current subjects did two identical calf press workouts on a flywheel ergometer. The following three variables were obtained from workouts–the total work (TW) performed, net energy costs, and peak blood lactate concentration ([BLa−]). With multivariate regression, four variables correlated with each criterion measures’ variance–lower leg length (LLL) and cross-sectional area (CSA), as well as the lengths of the triceps surae (ML) and Achilles tendon (ATL). Our predictor variables correlated to significant amounts of TW and net energy cost, but not [BLa−] variance. Univariate matrices showed CSA was the best overall predictor for our criterion measures, while ML and ATL were generally weaker correlates. ATL did not have as great an impact as with other lower leg exercises; likely because the slow rate of ankle joint movement greatly limited SEE activity. The limited degree of foot support for ergometer repetitions was also a factor that likely weakened ATL's impact as a correlate. More research on anatomy's impact on this novel form of exercise is warranted.

Objectives Space flight diets include a 55/30/15 (carbohydrate/fat/protein) ratio. Yet recent long-term missions require astronauts to exercise several hours daily for up to seven days a week. We hypothesize a high protein diet (45/25/30) is more conducive to longer missions and their high volumes of exercise. Methods With a within-subjects design, participants (8 men, 8 women) adhered to each diet for 14 days. Isocaloric diets were prescribed based on subject's resting metabolic rate, activity level and body composition. Compliance was monitored daily. Per subject, diet sequence was randomized to limit order effects. Immediately after each diet concluded subjects worked out on a gravity-independent device (Impulse Training Systems; Newnan, GA) while tethered to a metabolic cart. Workouts entailed four (unilateral knee extension, unilateral hip extension, unilateral standing row, bilateral arm pulldown) exercises, comprised of three 60-second sets separated by 60-second rests and done against 4.4 kg. Work volumes were measured from our device, as were pre-exercise respiratory quotients (RQ), and energy costs based on net O2 uptakes. Blood lactate concentrations ([BLa-]) were measured before and five minutes after workouts. Exercise and respiratory data were compared with 2(gender) × 2(diet) ANOVAs, with repeated measures for diet. [BLa-] were assessed with a 2(gender) × 2(time) × 2(diet) ANOVA, with repeated measures for time and diet. Results Significant [BLa-] differences occurred for time (post > pre) and for RQ by diet (55/30/15 > 45/25/30). Trends for work differences occurred by gender (men > women) and diet (45/25/30 > 55/30/15). Conclusions Our preliminary results concur with those that show greater RQ values from diets higher in carbohydrates. With continued data collection it is of interest to note if inter-work differences reach statistical significance, with higher values produced by the high protein diet. If so, such a diet may be more efficacious as a countermeasure to the muscle atrophy, strength loss and performance decrements for in-flight operational tasks seen with longer missions. Funding Sources Kentucky Space Grant Consortium.