Purpose Time-Resolved Near Infrared Spectroscopy (TR-NIRS) was used to quantify tissue oxy- and deoxy-hemoglobin concentrations ([HbO2], [HbR]), and O2 saturation (stO2) in the oblique fibers of the vastus medialis muscle (VMO) and brain prefrontal cortex (PFC) during knee extension with and without blood flow restriction (BFR). Methods Six young healthy males performed three sets of knee extensions on a dynamometer (50% 1 RM), separated by 90 sec rest periods, in three conditions: 1) until fatigue without BFR (Fatigue); 2) until fatigue with BFR (100 mm Hg cuff constriction around thigh, BFR); 3) same number of repetitions from condition 2, without BFR (Matched). Each condition was performed on a separate visit. Results BFR was associated with higher VMO [HbR] (rest 1: 57.8 μM BFR vs. 35.0 μM Matched, p < 0.0001) and a significantly lower stO2 during recovery periods between sets (7.5 – 11.2 % lower than non-BFR conditions for rest 1 and 2, p < 0.0001). Using a piecewise linear spline method, a spike in [HbR] was observed before the onset of HbR clearance during recovery, causing HbR clearance to begin at a higher concentration (BFR: 81 μM vs. Matched: 62 μM, p = 0.029). [HbO2] kinetics during recovery were also affected by BFR, with longer duration (BFR: 51 s, Matched: 31 s, p = 0.047) but lower rate of increase (BFR: 58 μM/min, Matched: 89 μM/min, p = 0.004) during recovery. In the PFC, BFR was associated with increased [HbR], diminished increase in [HbO2], and higher subjective exertion. Conclusions These findings yield insight into possible physiological mechanisms of BFR, and suggest a role of TR-NIRS in monitoring and optimization of BFR exercise on an individual basis.

The purpose of this study was to examine the affective responses to acute resistance exercise (RE) performed at self-selected (SS) and imposed loads in recreationally trained women. Secondary purposes were to (a) examine differences in correlates of motivation for future participation in RE and (b) determine whether affective responses to RE were related to these select motivational correlates of RE participation. Twenty recreationally trained young women (mean age = 23 years) completed 3 RE sessions involving 3 sets of 10 repetitions using loads of 40% of 1 repetition maximum (1RM), 70% 1RM, and an SS load. Affective responses were assessed before, during, and after each RE session using the Feeling Scale. Self-efficacy and intention for using the imposed and SS loads for their regular RE participation during the next month were also assessed postexercise. Results revealed that although the SS and imposed load RE sessions yielded different trajectories of change in affect during exercise (p < 0.01), comparable improvements in affect emerged after RE. Additionally, the SS condition was associated with the highest ratings of self-efficacy and intention for future RE participation (p < 0.01), but affective responses to acute RE were unrelated to self-efficacy or intention. It is concluded that acute bouts of SS and imposed load RE resulted in comparable improvements in affect; recreationally trained women reported the highest self-efficacy and intention to use the load chosen in SS condition in their own resistance training; and affective responses were unrelated to motivational correlates of resistance training.

Controversy exists regarding the safety and performance benefits of performing the squat exercise to depths beyond 90° of knee flexion. Our aim was to compare the net peak external knee flexion moments (pEKFM) experienced over typical ranges of squat loads and depths. Sixteen recreationally trained males (n = 16; 22.7 ± 1.1 yrs; 85.4 ± 2.1 kg; 177.6 ± 0.96 cm; mean ± SEM) with no previous lower limb surgeries or other orthopedic issues and at least one year of consistent resistance training experience while utilizing the squat exercise performed single repetition squat trials in a random order at squat depths of above parallel, parallel, and below parallel. Less than one week before testing, one repetition maximum (1RM) values were found for each squat depth. Subsequent testing required subjects to perform squats at the three depths with three different loads: unloaded, 50% 1RM, and 85% 1RM (nine total trials). Force platform and kinematic data were collected to calculate pEKFM. To assess differences among loads and depths, a two-factor (load and depth) repeated-measures ANOVA with significance set at the P < 0.05 level was used. Squat 1RM significantly decreased 13.6% from the above parallel to parallel squat and another 3.6% from the parallel to the below parallel squat (P < 0.05). Net peak external knee flexion moments significantly increased as both squat depth and load were increased (P ≤ 0.02). Slopes of pEKFM were greater from unloaded to 50% 1RM than when progressing from 50% to 85% 1RM (P < 0.001). The results suggest that that typical decreases in squat loads used with increasing depths are not enough to offset increases in pEKFM.

Purpose To examine the effect of a high-intensity concurrent training program utilizing a single gravity-independent device on maintaining skeletal muscle function and aerobic capacity during short-term unilateral lower limb suspension (ULLS). Methods Nineteen subjects (10 male; 9 female; 21.0 ± 2.5 yr, 65.4 ± 12.2 kg) were separated into 2 groups: 1) 10 day unilateral lower limb suspension only (ULLS; n = 9) and 2) 10 day ULLS plus aerobic and resistance training (ULLS+EX; n = 10). Exercise was performed on a single gravity-independent Multi-Mode Exercise Device (M-MED) with alternating days of high-intensity interval aerobic training and maximal exertion resistance training. Results Aerobic capacity increased by 7% in ULLS+EX (P < 0.05). Knee extensor and ankle plantar flexor three repetition max increased in the ULLS+EX group (P < 0.05) but this change was only different than ULLS in the plantar flexors (P < 0.05). Peak torque levels decreased with ULLS but were increased for the knee extensors and attenuated for the ankle plantar flexors with ULLS+EX (P < 0.05). A shift towards type IIx myosin heavy chain mRNA occurred with ULLS and was reversed with ULLS+EX in the vastus lateralis (P < 0.05) but not the soleus. Myostatin and atrogin increased with ULLS in both the vastus lateralis and soleus but this change was mitigated with ULLS+EX only in the vastus lateralis (P = 0.0551 for myostatin; P < 0.05 for atrogin). Citrate synthase was decreased in the soleus during ULLS but was increased with ULLS+EX (P < 0.05). Conclusion These results indicate that an M-MED class countermeasure device appears to be effective at mitigating the deconditioning effects of microgravity simulated during a modified-ULLS protocol.