Critical load: a novel approach to determining a sustainable intensity during resistance exercise.

BACKGROUND: A hyperbolic function as well as a linear relationship between power output and time to exhaustion (Tlim) has been consistently observed during dynamic non-resistive exercises. However, little is known about its concept to resistance exercises (RE), which could be defined as critical load (CL). This study aimed to verify the existence of CL during dynamic RE and to verify the number of workbouts necessary to determine the optimal modeling to achieve it. METHODS: Fifteen healthy men (23±2.5 yrs) completed 1 repetition maximum test (1RM) on a leg press and 3 (60%, 75% and 90% of 1RM) or 4 (+ 30% of 1RM) workbouts protocols to obtain the CL by hyperbolic and linear regression models between Tlim and load performed. Blood lactate and leg fatigue were also measured. RESULTS: CL was obtained during RE and 3 workbouts protocol estimate it at 53% while 4 tests at 38% of 1 RM. However, based on coefficients of determination, 3 protocols provided a better fit than the 4-parameter model, respectively (R2>0.95 vs. >0.77). Moreover, all intensities increased blood lactate and leg fatigue, however, when corrected by Tlim, were significantly lower at CL. CONCLUSIONS: It was possible to determinate CL during dynamic lower limbs RE and that 3 exhaustive workbouts can be used to better estimate the CL, constituting a new concept of determining this threshold during dynamic RE and reducing the physically demanding nature of the protocol. These findings may have important applications for functional performance evaluation and prescription of RE programs.

Heart rate autonomic responses during deep breathing and walking in hospitalised patients with chronic heart failure.

OBJECTIVE: To evaluate the acute effect of physiotherapy (deep breathing exercises and walking) on heart rate variability in patients hospitalised with chronic heart failure (CHF). DESIGN: Ten males with CHF (57 ±â€Š7 years) and 10 healthy controls (59 ±â€Š9 years) were included. Heart rate and RR intervals were recorded in the following conditions: supine, seated, during deep breathing exercises and during and after walking. Heart rate variability was analysed by linear and non-linear methods (α2, Mean HR, rMSSD, SDNN and ApEn). RESULTS: Patients presented significantly lower SDNN (12.4 ±â€Š4 versus 26 ±â€Š8 ms), rMSSD (18.2 ±â€Š16.2 versus 25 ±â€Š19.5 ms) and ApEn (9.9 ±â€Š10 versus 16.68 ±â€Š22.6) during the walking compared to controls (p < 0.05). In addition, mean HR was significantly higher during and after walking for patients with CHF compared to controls (103 ±â€Š8 versus 80 ±â€Š2 bpm and 90 ±â€Š9 versus 68 ±â€Š2 bpm, respectively). Patients with CHF demonstrated a significant reduction of α2 during deep breathing (0.78 ±â€Š0.1) when compared to the seated position (1.08 ±â€Š0.1) and walking (1.15 ±â€Š0.2, p < 0.05). Additionally, rMSSD index increased during deep breathing when compared to walking in both groups. CONCLUSION: Deep breathing exercises and walking are safe and promote beneficial effects on heart rate variability in patients hospitalised for CHF.