Bouncing on Mars and the Moon—the role of gravity on neuromuscular control: correlation of muscle activity and rate of force development

Abstract

On our astronomical neighbors Mars and the Moon, bouncing movements are the preferred locomotor techniques. During bouncing, the stretch-shortening cycle describes the muscular activation pattern. This study aimed to identify gravity-dependent changes in kinematic and neuromuscular characteristics in the stretch-shortening cycle. Hence, neuromuscular control of limb muscles as well as correlations between the muscles' pre-activation, reflex components, and force output were assessed in lunar, Martian, and Earth gravity. During parabolic flights, peak force (F), ground-contact-time, rate of force development (RFD), height, and impulse were measured. Electromyographic (EMG) activities in the m. soleus (SOL) and gastrocnemius medialis (GM) were assessed before (PRE) and during bounces for the reflex phases short-, medium-, and long-latency response (SLR, MLR, LLR). With gradually decreasing gravitation, F, RFD, and impulse were reduced, whereas ground-contact time and height increased. Concomitantly, EMG_GM decreased for PRE, SLR, MLR, and LLR, and in EMG_SOL in SLR, MLR, and LLR. For SLR and MLR, F and RFD were positively correlated to EMG_SOL. For PRE and LLR, RFD and F were positively correlated to EMG_GM. Findings emphasize that biomechanically relevant kinematic adaptations in response to gravity variation were accompanied by muscle- and phase-specific modulations in neural control. Gravitational variation is anticipated and compensated for by gravity-adjusted muscle activities. Importantly, the pre-activation and reflex phases were differently affected: in SLR and MLR, SOL is assumed to contribute to the decline in force output with a decreasing load, and, complementary in PRE and LLR, GM seems to be of major importance for force generation.

Anticipation of drop height affects neuromuscular control and muscle‐tendon mechanics

“…However, when information about the drop height is uncertain or unknown, neuromuscular activity and muscle shortening are reduced dramatically prior to GC in the unknown vs known vs cheat condition by approximately 10% (Tables and ). This is in accordance with prior studies that found reduced pre‐activation in conditions where subjects were faced with unpredictability in jumping or landing tasks and impact loads induced by altered gravity . Thus, it seems to be a general phenomenon that when the motor system is not able to adequately predict the loading, pre‐activation is reduced .…”

“…Two aspects might be important in interpreting these findings. The first aspect deals with proactive modulations prior to the event of GC, and the second aspect with the compensatory reactions after touch‐down . The next sections will discuss both aspects in detail.…”

“…Ground reaction forces were used to determine peak force and GCT (time interval between GC and take‐off). RFD (force during the first 50 ms of GC divided by 50 ms) as a reactive index and jump height (H, H = g*t 2 /8, with t = flight time from the instant of take‐off to landing, g = 9.81 m s −2 ) were calculated …”

“…These specific latencies were chosen based on GM fascicle lengthening occurring at GC. Subsequently, iEMGs were time‐normalized to 1 second [mVs] to make them comparable between phases and then normalized to the respective MVC . Furthermore, co‐activation of TA and GM (TA/GM) was calculated for PRE as well as SLR, MLR and LLR phases.…”

Human Biomechanical and Cardiopulmonary Responses to Partial Gravity – A Systematic Review

“…One of the most recent studies about musculoskeletal changes due to partial gravity exposure is the study of Ritzmann et al ( 2016 ) which is not included in this systematic review because it was not published during the time of the present literature search. The authors measured biomechanical parameters of a bouncing movement (often referred to as skipping) during a partial gravity parabolic flight (Mars and Moon parabolas).…”